388 JOHN BEARD, 



entirely sensory in nature. The presence of ganglion-cells in the 

 myotome, as well as the passage of nerves into that structure, — for 

 at that time it had not been recognised that such nerves usually pass 

 through the myotome, if they enter it, — seemed to indicate a mo- 

 torial function for a part of the apparatus. That view is, after mature 

 consideration, entirely abandoned, and in its present condition a 

 sensory function is ascribed to the system. At the same time, the 

 presence of ganglion-cells in the myotome requires explanation. Those 

 which lie, as many of them do, in the outer epithelium may possibly 

 owe their position there to the genetic relations ^ ) of this layer to 

 the cutis, as established by Hatschek, Ziegler, Van Wijhe and 

 Rabl. 



Does this explain all such instances? There may be some, — 

 and in this connection Figs. 42, 55, 93 and 94 may be referred to, 

 — which at all stages are perhaps in a state of degeneration (in that 

 they are apparently quite destitute of processes), and whose former 

 motorial nature is quite possible. Such cases could be explained on the 

 assumption that formerly there was a motor part of the apparatus, 

 now entirely degenerated. They, or some of them, may be erratic 

 bits of such. However, this is rather speculative, and there is no 

 wish to do more than express the opinion that some very slight 

 portion of the system may be so viewed. 



In an interesting paper (No. 15) Prof. Strasser has reviewed 

 my former statements, and has expressed himself emphatically in favour 

 of a sensory function of the apparatus. I do not propose to follow 

 his arguments (p. 745 — 748), but note the present agreement of 

 our conclusions, though based on different premisses. To my mind 

 the general course of the nerves under the epiblast, as well as the 

 appearances depicted in Figs. 25 and 55 are very significant facts in 

 support of this view. 



3. Degeneration of the transient apparatus. 



It has now been demonstrated that in the skate embryo (whether 

 belonging to it or not is a question for subsequent consideration), 

 there arises a system of ganglion-cells and simple nerves at a very 

 early period of the development. It rapidly matures, and experiences 



1) At the same time any supposition that they are therefore con- 

 stituents of the embryo, as opposed to the larva, must be guarded 

 against. 



