334 DEVELOPMENT OF ELASMOBRANCH FISHES. 



any change, and it becomes converted into the main dorso-lateral 

 muscles of the body, which apparently correspond with the 

 muscles derived from the whole muscle-plate of the Elasmo- 

 branchs. From the inner layer of the splanchnic division there 

 are next formed the main internal ventral muscles, rectus 

 abdominis, &c., as well as the chief connective-tissue elements of 

 the parts surrounding the spinal cord. The outer layer of the 

 vertebral plates forms the dermis and subcutaneous connective 

 tissue, as well as some of the superficial muscles of the trunk 

 and the muscles of the limbs. 



Dr Gotte appears to think that the vertebral plates in Am- 

 phibians present a perfectly normal development very similar 

 to that of other Vertebrates. The divergences between Am- 

 phibians and other Vertebrates appear, however, to myself, to be 

 very great, and although the very careful account given by Dr 

 Gotte is probably to be relied on, yet some further explanation 

 than he has offered of the development of these parts amongst 

 the Amphibians would seem to be required. 



A primary stage in which the two layers of the vertebral 

 plates are continuous with the somatic and splanchnic layers 

 of the body-wall is equally characteristic of Amphibians, Elasmo- 

 branchs and Mammals. In the subsequent development, how- 

 ever, a great difference between the types becomes apparent, for 

 whereas in Elasmobranchs both layers of the vertebral plates 

 combine to form the muscle-plates, out of which the great dorso- 

 lateral muscles are formed, in Amphibians what appear to be 

 the equivalent muscles are derived from a few of the cells (the 

 kernel) of the inner layer of the vertebral plates only. The cells 

 which form the lateral muscles in Amphibians might be thought 

 to correspond in position with the cells which become, in Elas- 

 mobranchs, converted into the special early formed band of 

 muscles (m.p'.}, rather than, as their development seems to 

 indicate, with the whole Elasmobranch muscle-plates 1 . 



1 The type of development of the muscle-plates of Amphibians would become 

 identical with that of Elasmobranchs if their first-formed mass of muscle corresponded 

 with the early-formed muscles of Elasmobranchs, and the remaining cells of both 

 layers of the protovertebrse became in the course of development converted into 

 muscle-cells indistinguishable from those formed at first. Is it possible that, owing 

 (o the distinctness of the first-formed mass of muscle, Dr Gotte can have overlooked 



