摘要:

AbstractWhat is here called Fisher's axiom states that all large mutations are deleterious, and the consequence of this is the generally accepted Darwinian notion that all evolutionary progress must have occurred through the accumulation of small mutational steps. We have in the present paper tested the postulate that one parameter, namely, the body size (weight or volume) does not vary in this way, but rather in steps which are powers of two, up to or down, as the case may be. The outcome of our analysis is that this hypothesis is corroborated with fair significance for certain, randomly selected, groups of living and extinct animals. The consequences of this observation are briefly discussed.

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1974.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractH. serriferais described and supplementary information given onH. boehmigi. The material of both species was collected from the brood pouch of amphipods,H. serriferafromOrchomene no‐dimanus(Walker). The studies complete our general picture of the anatomy of the genusHypoblepharinaand support the theory that all the species of this genus are commensals in amphipod

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1974.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractEggs ofGyrocotyle urnaspecimens were hatched. Certain results from the hatching work are given. The protonephridial system of the larvae/lycophores was investigated. The system was found to be bilaterally symmetrical with two nephridiopores in the anterior body‐half. The system is very similar to the posterior protonephridial system in the oncomiracidium (the monogenoidean larva). Unlike the oncomiracidium theGyrocotylelycophore has no anterior system. The hooks of amphilinidean and gyrocotylidean lycophores were found to be of the same basic type as those of other cercomero‐morphaean larvae. A preliminary investigation of the hook ontogeny ofAmphilina foliaceawas made: all ten hooks appear to begin developing at the same time, the six ordinary hooks early assumed a similar shape and arrangement to those in the oncosphaera, the four aberrant hooks seem to be less aberrant in their earlier developmental stages. On a basis of the number of hooks and other facts relating to the larvae, cercomero‐morphaean evolution at the larval level is claimed. Because there are no traces of a mouth, a pharynx and an intestine in the ontogeny ofGyrocotyle, the lack of these body parts in the lycophore is assumed to be a primitive condition. It is claimed that the monogenoidean protonephridial system originated from a system of theGyrocotylelycophore type and that the mouth, pharynx and intestine are secondarily evolved in the monogenoideans. It is assumed that mouth‐, pharynx‐ and intestine‐less creatures with an ingestive body‐covering gave rise to the digenean and the cercomeromorphaean evolutionary lines. On a basis of the ontogeny and the life cycles in the different cercomeromorphaean groups it is claimed that the adult monogenoideans never reached a certain evolutionary level which is repeated in the ontogeny of the ces‐todes, the amphilinideans and the

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1974.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractThe intrinsic and extrinsic musles inCytheridea papillosaare described and their function discussed. Special attention has been paid to the extrinsic muscles and the scars these muscles form on the valves. Two scars, close together, in the central area, earlier referred to as frontal or an‐tennal scars, have muscular origin. The larger of these belongs to the carapax adductor system, and the namefrontal adductor muscle scaris suggested for it. The smaller scar is associated with the mandible, whose muscle acts as an abductor. The namemandibular abductor muscle scaris suggested for i

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1974.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractA comparative study of the sensory line system and the lateralis nerve complex in osteostracans on one hand, and in petromyzontids on the other, reveals further similarities between these two groups. The interrelationships between the lateralis nerve complex and the other cranial nerves in osteostracans lead to the conclusion that, in these forms, the first, second and third branchial nerves correspond respectively to the ramus maxillaris trigemini, the ramus mandibularis trigemini and the facialis of petromyzontids.RésuméL'étude comparative des lignes sensorielles et du complexe du nerf latéral chez les Ostéostracés et les Pétromyzontides révele A nouveau de grandes similarités entre ces deux groupes. En outre, les rapports anatomiques entre le complexe du nerf latéral et les autres nerfs crâniens conduisent a la conclusion que les trois premiéres paires de nerfs branchiaux des Ostéostracés correspondaient respectivement aux rameaux maxillaire et mandibulaire du trijumeau ainsi qu'au nerf facial chez les P

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1974.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY