386 MONTGOMERY. [Vol. XIII. 



Burger ('90b, p. 107) describes a modification of these cells, 

 "welche sich durch etwas grossere Kerne und lebhaf teres 

 Hervortreten des Zellplasmas von jener unterscheidet," andare 

 situated around the cephalic clefts; but I have been unable to 

 find any structural distinction between these two. However, 

 two modifications of cells I may be distinguished as follows : 



(a) A group of cells on the medio-dorsal side of the brain 

 lobe, situated a little behind a frontal plane passing through 

 the first ventral commissure. Their nuclei average larger, are 

 as a rule more elongate-oval in form, and stain less deeply than 

 the following. 



(b) The greater number of the cells I on the dorsal brain 

 lobe, i.e., all with the exception of those in group (a); they 

 have typically (though not always) spherical, deeply staining 

 nuclei. But there is only a slight degree of difference between 

 these two modifications, and intergradations are found between 

 them. 



In Cerebratulus these cells do not differ appreciably from 

 those of Lmeiis, and occur in the same two modifications 

 (Fig. 17 a, b). 



B. Cell II. 



Lineus gesserensis (Fig. 2). — These cells are usually more or 

 less elongated, pear-shaped, with the greatest diameter proxi- 

 mally, becoming distally gradually more slender ; seldom have 

 they a shortened, oval form. The more or less centrally placed 

 nucleus contains a relatively smaller amount of chromatin than 

 that of I and III, and differs from the latter further in its 

 elongate-oval, and not spherical, shape. One nucleolus (/z) is 

 sometimes found in it. The cytoplasm is of a coarsely vacuolar 

 structure; sometimes the hyaloplasm fills the whole proximal 

 portion of the cell as far as the nucleus. But a thin, peripheral 

 layer (Alv.) of spongioplasm is always present, and a similar 

 layer envelops the nucleus; these two layers, which may repre- 



fibrillar structure of the spongioplasm of the ganglion cells. Further, these terms 

 can be applied to denote the more fluid contents of the less fluid meshwork in 

 describing a " honeycombed " structure of protoplasm (though Biitschli, '94, has 

 endeavored to avoid the use of any such descriptive terms as might imply a differ- 

 ence between the substance of the meshwork and the substance contained within it). 



