摘要:

Spermatozoa ofSergentomyia minutawere examined by light, scanning, and transmission electron microscopy. They were seen to be formed by a head and a tail. The head was characterized by an acrosomal complex with a thin space containing granular material organized as in a perforatorium. The tail contained a “9 + 9 + 0”; axoneme and one mitochondrial derivative. A comparison with the spermatozoon ultrastructure of other Diptera, particularly Psychodidae, is discussed.

ISSN:0373-4137    

DOI:10.1080/11250009209386692

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The tubificid oligochaeteClitellio arenariusproduces two kinds of spermatozoa which group to form spermatozeugmata in the spermathecae. The fertilizing (typical) spermatozoa, forming the core of the spermatozeugmata have: an acrosome with a deeply withdrawn acrosome vesicle and an acrosome rod; a long nucleus apically twisted and basally straight; five small mitochondria forming the middle piece; a fully transformed centriole; a flagellum with a central axonemal apparatus showing a ≪prominent central sheath≫ tract, followed by a ≪tetragon fibre≫ tract, and by a conventional (two singlets) tract; plasma membrane at a short distance from the axoneme. The atypical spermatozoa, forming the cortex of the spermatozeugmata, show a small acrosome, in which the acrosome vesicle is external to the tube, and lacks a rod; a small thread‐like nucleus; a middle piece formed by three large mitochondria; a partly untransformed centriole; a flagellum with conventional axoneme and plasma membrane largely separated from the axoneme. It is possible to distinguish morphologically the two sperm lines in early spermiohistogenesis: pycnotic nuclei are present in the cytophores of the atypical line and the microtubular manchette surrounding the early spermatids is incomplete. It is proposed that the spermatozeugmata ofClitellioare more plesiomorphic than those ofTubifex.A heterochronic mechanism may be responsible for the differentiation of the two sperm lines.

ISSN:0373-4137    

DOI:10.1080/11250009209386693

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The life‐cycle of the abundant and frequent calanoid copepodAcartia(Paracartia)latisetosais not completely known. Eggs of three morphological types and at least two biological meanings were obtained from adult specimens under laboratory conditions. Two types (≪smooth≫ and ≪brush‐like≫) were subitaneous. A third, ≪spiny≫, type rested for at least 50 days before hatching and was considered diapausal. It was suggested that the production of these different types of eggs helpsA. latisetosato overcome periodic, or unpredictable, crises typical of the confined brackish environments where this species is abundant. This is the first record of a resting stage inA. latisetosa.

ISSN:0373-4137    

DOI:10.1080/11250009209386694

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The relationship between mating speed, an important component of fitness, and wing length has been analyzed inDrosophila malerkotliana.Flies mating first have longer wings than non‐mating flies. Age has no detectable effect on the relationship between mating speed and body size.

ISSN:0373-4137    

DOI:10.1080/11250009209386695

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Arrangement and morphology of teeth in larval and metamorphicTriturus vulgaris meridionaliswere studied at the scanning electron microscope and compared with adult and neothenic newts. Monocuspid larval teeth are monostichous on margin of jaws and polystichous on palatine and coronoid bone. They are substituted during metamorphosis by bicuspid teeth arranged in a single row on margin of the jaws and in a double row on the vomerine bones. Bicuspid teeth have initially the same shape but later are dimorphic, according to their distribution in the mouth. The variation of tooth morphology is discussed and correlated with feeding strategies.

ISSN:0373-4137    

DOI:10.1080/11250009209386696

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The male cloacal regionof Salamandra s. giglioliiis examined by light microscopy. The cloacal cavity exhibits a complex architecture consisting of typical outfoldings and recesses, which correspond to the secretion sites of specific accessory glands. These are the dorsal, pelvic, Kingsbury's, and ventral glands. The hypertrophy of these secretory components, particularly of the dorsal and ventral ones, contributes to form the cloacal swelling of the male during the reproductive season. The morpho‐functional characteristics of the cloacal structures inSalamandraare discussed in comparison with members of the same and other urodele families.

ISSN:0373-4137    

DOI:10.1080/11250009209386697

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The fat body of the female stick insect,Bacillus rossius(Rossi), was examined ultrastructurally in developing larvae. Two different fat body tissues are present in first instar larvae: A remnant of an embryonic tissue, and a newly differentiated tissue appearing only after hatching, the larval fat body. The embryonic fat body consists of large cells with numerous lipid droplets of saturated fatty acids. They are randomly dispersed in a dense cytoplasm packed with free‐ribosomes. The larval fat body includes cells highly enriched in glycogen and with numerous unsaturated lipid droplets. With the proceeding of development, the embryonic fat body is destined to disappear. By contrast, the larval fat body undergoes progressive decrease in glycogen content, and the cytoplasm gradually fills with numerous Golgi apparatus and cisternae of the rough endoplasmic reticulum. Lipid droplets remain in the larval fat body until the transition to the adult stage takes place. With the attainment of the stage II of development, composite secretory granules appear in relevant number in the cell cytoplasm. Initially, they retain a random distribution in the cell cytoplasm, but later move to the apical cell surface by stage III. By stage IV, the fat body cell surface comes to be characterized by an extensive plasma membrane reticular system that projects onto the basal lamina. Following transition to the adult stage and disappearance of the lipid droplets from the tissue, the cell cytoplasm comes to manifest a clear apico‐basal polarity. Composite secretory granules are thus seen to pile up in the apical cytoplasm, following a progressive sequence of maturation from the Golgi apparatus. These observations allow the conclusion that fat body cells inB. rossiusmake use of the same secretory pathway leading to formation of composite secretory granules, irrespective of the haemolymph protein being secreted during larval development.

ISSN:0373-4137    

DOI:10.1080/11250009209386698

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Drosophilaembryos exposed to diazepam showed an abnormal centrosome function. Mitotic progression was altered and the migration of the nuclei towards the embryo surface was irregular. Cleavage furrow formation was also affected, large cortical areas failing to cellularize.

ISSN:0373-4137    

DOI:10.1080/11250009209386699

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Preliminary data showed evidence that mating type I and mating type II cells ofParamecium primaurelia,at the onset of the mating reactivity of the cultures, form different numbers of food vacuoles. The authors now investigate whether the differences in vacuole formation are visible at the beginning of culture growth, or whether they occur only later. Data collected during various stages in the early life of a clone, before mating reactivity develops, show higher food vacuole numbers per cell in mating type II cells than in mating type I cells. The difference in numbers of the two mating types disappears, and then the values reverse with starvation of the culture. These results are in agreement with previous data on the growth of complementary mating type cell lines, showing that different mean rates of growth characterize the two mating types during culture life.

ISSN:0373-4137    

DOI:10.1080/11250009209386700

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The carrion and the hooded crow (Corpus corone coroneandCorvus c. comix) are usually considered as morphs of a single species. They have parapatric distributions with narrow belts of overlap where fertile hybrids are produced. This three‐year study analyzed the variation of egg volume, and of chick growth and survival among allopatric parental populations and phenotypically parental and hybrid sub‐populations in a hybrid zone. Hybrid females laid eggs significantly smaller than those of parental females, living both in areas of sympatry and allppatry. No differences in chick growth were observed between pairs of different composition in the hybrid zone. Nestlings in the hybrid zone were significantly lighter than those in allopatric areas at all ages, and grew to a lower asymptotic weight. Tarsus grew faster and to a higher asymptote in the carrion crow area than in the hooded crow and in the hybrid areas. Chick survival was significantly influenced by female but not by male phenotype. Chicks in hybrid female nests had a comparatively low survival rate. The results indicated that, overall, crows in the hybrid zone are less fit than crows in allopatric areas. In particular, some hybrid females appear to be inferior to parental ones in their laying performance and their chicks are less surviving. The coincidence of the hybrid zone with an ecotone suggests that environmental factors could be effective in determining the observed pattern of variation in the breeding parameters considered.

ISSN:0373-4137    

DOI:10.1080/11250009209386701

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor