164 
J. BEARD. 
ELASM0BRANCHI1. 
The researches on this group were made on embryos of Tor- 
pedo ocellata, Pristiurus melanostomus, Acanthias 
vulgaris, Mustelus lsevis, and Scyllium canicula. Of 
the first-named form especially a very large and complete 
series of stages was at my disposal. This genus, Torpedo, is, 
in my experience, the best suited for researches on the early 
development, for the cell elements are larger, and the appear- 
ances presented in sections much clearer than those of any of 
the other forms mentioned. Of the other forms a sufficient 
number of stages was at my disposal to show that there is no 
essential difference in the development. And, in fact, for 
both cranial and spinal ganglia of all the Vertebrates which 
have till now come into my hands, including Teleostei, Rana, 
and even the Chick, I may with full confidence say that the 
appearances presented are all easily reducible to one type — to 
that of the Elasmobranchii. 1 The differences observed in 
different forms are in reality very slight, and are readily ex- 
plicable as variations in the time of development. As in the 
case of other organs, the development may be either retarded 
or accelerated. As a striking example of the way in which, for 
instance, the spinal ganglia agree in development in Torpedo 
and the Chick, I may mention that in sketches of portions of 
sections of the two forms drawn under high power it is often 
difficult, if not impossible, to find any differences, even in 
detail; and if the reader will compare figs. 37 a, 42, and 68, 
69, he will, I think, find it impossible of his own knowledge to 
say definitely that the former are figures of Torpedo sections, 
the latter of Chick sections. 
a. Spinal Ganglia of Elasmobranchii. 
Balfour is mainly responsible for our knowledge of the 
development of the spinal nerves and ganglia in Elasmo- 
branchs (Nos. 1, 2, and 3). 
1 The development in Ganoids conforms exactly to that in other types. 
