1893.] 



Presents. 



391 



motor cells is represented in fig. 4. It was drawn from a section of 

 the cord (of the same fish from which fig. 1 was taken), about six 

 inches in front of the electric organ. It closely resembles, except in 

 size, the electric cell (fig. 1), and it also resembles the large motor 

 cells of the Mammalian cord. A motor cell from the spinal cord of 

 a Mammal, drawn to the same scale as the other cells given, is repre- 

 sented in fig. 5.* This cell, smaller than the electric cell of the 

 Skate (1), and still smaller than the cell from Torpedo (3), is about 

 the same size as the electric cell of Gymnotus (2). 



With the help of sections through a series of embryo Skate, for 

 most of which I was indebted to Dr. Beard, I have been able to 

 study the development of the cells in the Skate's electric centre. This 

 part of the subject, together with the condition of the electric cells in 

 large fish, will be dealt with in a subsequent communication. It may, 

 however, be stated now : 1. That in B. batis embryos under 5 cm. 

 in length none of the motor cells in the caudal region have under- 

 gone enlargement. 2. That in an embryo 5 '8 cm. in length, although 

 the muscular fibres seemed still unchanged, certain cells in the 

 anterior horn of the caudal portion of the cord were distinctly larger 

 than similarly shaped cells in their vicinity. 3. That in an embryo 

 155 cm. in length, in which the electrical elements were already 

 well developed, the electric nerve-cells were large and conspicuous, 

 so that sections through the cord in the region of the electric organ 

 presented quite a different appearance from sections through the 

 root of the tail, where no change had taken place in the cells of the 

 anterior horn. 



Presents, April 27. 1893. 



Transactions. 



Adelaide : — Royal Society of South Australia. Transactions and 

 Proceedings. Vol. XIV. Part 2. 8vo. Adelaide 1891. 



The Society. 



Baltimore : — Johns Hopkins University. Circular. Vol. XII. 

 No. 104. 4to. Baltimore 1893 ; Studies in Historical and 

 Political Science. Series II. Nos. 3 — 4. 8vo. Baltimore 

 1893. The University. 



Berlin :— GeseMschaft fur Erdkunde. Zeitschrift. Bd. XXVII. 

 No. G. 8vo. Berlin 1892. The Society. 



Beziers : — Societe d'Etude des Sciences Naturelles. Bulletin. 

 Conipte-Rendu des Seances. Vol. XIV. 8vo. Beziers 1892. 



The Society. 



* For the use of the section from which fig. 5 was drawn I am indebted to Sir 

 William Turner, F.R.S. 



