REPORT ON THE NEMERTEA. 139 



disappeared, and which are only now retained in the ontogenetic development"; then 

 (p. 43) " for the Gasserian ganglion there is no indication of a connection with the 

 epiderm"; and, lastly (p. 52), "it appears to be hardly any longer possible to look 

 upon these nerve-ganglia (Nervenknoten) as simply homologous with spinal ganglia." 



Baldwin Spencer ^ writes (he. cit., p. 129) concerning Rana temporaria: — "Along 

 certain lines the cells of the nervous layer proliferate, and it is by this proliferation that 

 the rudiments of the cranial nerves are laid down" ; further (p. 130), "the development 

 of the ganglia at the level of the lateral line, and the fact of their long connection with 

 the epiblast at this point .... is of great interest in connection with certain 

 points in the development of the Elasmobranch nerves." 



Concerning the developmental phenomena in the trunk-region at this period, the spinal 

 nerves are stated to be not yet visible, " though the nervous sheath is clearly developed 

 and in this the lateral line " 



The author next mentions observations made by him on Dr. Beard's sections of 

 Elasmobranch embryos, and goes on to say {loc. cit., p. 131) : — 



" The Gasserian ganglion is, at all events in part, formed directly from the epiblast 

 the same development takes place in the case of the ganglion of the third and 

 seventh nerve — in that of the ciliary ganglion the development is particularly clear — 

 . . The ganglia arise along a level of the lateral line continued on the head." 



He next says : — " The curious origin of the ganglia of the cranial nerves points 

 strongly to the conclusion that .... their present condition and nature must 



. . . be regarded as a secondary and certainly not primitive condition. 



" In passing, I may just notice that on this supposition an explanation is oflfered as 

 to the origin and meaning of the two curious branches which unite respectively the 

 ganglia of the fifth and seventh and fifth and third cranial nerves ; they may be regarded 

 as persistent parts of the lateral nerve .... in the head." 



In the third place, extracts will be given from Beard's more extensive paper.^ He 

 writes (p. 97) as an introductory statement : — " At present we are acquainted with no 

 Invertebrate nervous system which is built upon the same plan as that of Vertebrates "; 

 and then passes to the results of his investigations chiefly carried out on embryos of 

 Torpedo and a few other Elasmobranchs. I make the following selections (p. 101) : — 



" At the point of fusion " (of the cephalic nerve with the epiblast) " a local thickening 

 of epiblast has previously taken place. After the fusion has taken place a proliferation 

 of some of the cells composing the thickening ensues. The proliferated cells form a mass 



of actively-dividing elements still connected with the skin This mass of 



cells is the rudiment of the ganglion of the dorsal root." 

 . On p. 110 he adds :—" Along with the separation of the (vagus) ganglion from the 



' Early Development of Rana temporaria, Quart. Journ. Micr. Scl, Suppl., 1885. 



2 Branchial Sense-Organs in Ichthyopsida, Quart. Journ. Micr. Sci, November 1885, No. cL 



