No. 3.] STUDIES ON THE HETERONEMERTINI. 403 



I have found only three or four cells containing two nucleoli 

 apiece, and in each case the latter were unequal in size; these 

 cells were placed about the middle of the lateral chords. Thus, 

 it is not the case in C. lactetcs that "die Zellen im hinter- 

 sten Ende der Seitenstamme besitzen . . . haufig zwei gleich 

 grosse Nucleoli," as Burger ('90b, p. 117) has stated for C. 

 marginatiis; on the contrary, I found the most posterior cells 

 to contain only one nucleolus. Nor yet, in the species described 

 here, are the nucleoli of the first pair of neurochord cells in the 

 brain directed towards one another. 



The cell (Figs. 27-29, 31) is usually of a shortened, pyriform 

 shape, occasionally nearly spherical, or again elongated (this is 

 the case with the first pair in the brain). The cell, together 

 with the thickened, proximal portion of its nerve tubule, often 

 resembles an Italian wine-flask. As a rule, though not always, 

 these cells are much larger than III. 



The cytoplasm is, especially distally, coarsely vacuolar, more 

 so than in any other ganglion cell ; this gives the cell much the 

 same appearance as a slime-producing gland cell. It is char- 

 acteristic for the neurochord cells that the hyaloplasm {HI. PI.) 

 usually stains slightly with haematoxylin. There is always 

 a fine-grained, peripheral, spongioplasmic, supposedly alveolar 

 layer, and a similar layer immediately invests the nucleus (Alv.). 

 The mass of cytoplasm is never finely granular throughout, 

 such as is sometimes the case in III, but the distal portion at 

 least is always vacuolar; and as in III, there is no special 

 linear, radial, or concentric arrangement of the hyaloplasmic 

 vacuoles. In IV also the general structure of the cytoplasm 

 apparently corresponds to that of a honeycombed meshwork 

 (Butschli, '94). 



E, Comparison of the Ganglion Cells. 



In Linens the ganglion cells are not so strongly differentiated, 

 i.e., represent a lower stage of development than in Cerebratulus. 

 Thus in the former genus there are no neurochord cells, and 

 the cells II and III approximate much more closely than in 

 the latter. 



