404 ■ MONTGOMERY. [Vol. XIII. 



In both these genera cell I differs markedly from the others 

 in (i) its small size, (2) the relatively great size of its nucleus, 

 and its large proportion of chromatin (Figs, i, 17). Burger 

 ('90b, '91b) has shown these cells to be sensory in function, 

 which their position, etc., renders very probable. 



The cell III in structure closely resembles II, especially 

 in Linens. Cell III (Figs. 3-16, 19-21, 29, ///) is structurally 

 intermediate between II and IV, and even grades into them ; 

 while II (Figs. 2, 18) and IV (Figs. 27-29, 32) never inter- 

 grade, but are always to be sharply distinguished. 



Ill resembles II in: (i) its usually elongated form, (2) its 

 more or less marked radial arrangement around the fibrous 

 core (in Linens it is occasionally even grouped in radial clus- 

 ters), (3) in the usually central or distal position of the 

 nucleus. 



Ill resembles IV in: (i) its size (very large examples being 

 fully as large as small specimens of IV), and (2) in the usually 

 peripheral distribution of the chromatin within the nucleus. 

 Some cells intermediate in structure between III and IV occur 

 in the lateral chords. Thus the cell reproduced in Fig. 23 

 resembles IV in the coarse vacuolization of its cytoplasm, and 

 in the peripheral, proximal position of its nucleus; but it is 

 similar to III in its small size, the arrangement of the chromatin, 

 and the position of the nucleolus within the nucleus. 



Since it is the rule in most of the higher Metazoa that the 

 larger ganglion cells are motor cells, and since III, which is 

 the largest cell in Limits and next to the largest in Cerebrattihis, 

 shows structural resemblances to II on the one hand, and to 

 IV on the other, I would conclude that these three types of 

 cells are related in function, as well as in structure, and that 

 they are probably all motor cells. Burger ('9lb, '95) has already 

 produced good evidence to show that IV cannot be sensory 

 cells, since he found that their axis cylinders do not pass out 

 of the lateral chords ; and having found that they occur only in 

 genera which have the power of swimming, he makes the sug- 

 gestion that they are directly concerned in this form of motion. 

 I give the following diagram to represent my views on the 

 morphological and physiological, though not necessarily histo- 



