No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 475 



caused by (i) the direct action of the fluid of Flemming, or 

 more probably (2) they might be post-mortem exudations of the 

 nucleoli, which might well be produced before the slowly pene- 

 trating fixative had reached to the cells in question. At any 

 rate, they cannot be regarded as normal structures. Do they 

 represent the " Kernkorperchenkreis " of Eimer } 



The chromatin, as in Doto, occurs in the form of granules, 

 which are connected by fine fibers. After fixation with Klein- 

 enberg's fluid a clear space encloses each nucleolus {Figs. 93 

 and 94); but this space is not to be found after fixation in 

 other fluids. 



As in Doto, the nuclei of the colossal ganglion cells contain 

 a relatively greater amount of nucleolar substance than do those 

 of the second and third types. But in the former genus there are 

 in the colossal cells from about six to thirteen nucleoli, and these 

 vary noticeably in size and structure, while in Montagna there 

 are only from one to three, which are always homogeneous and 

 usually quite equal in dimensions. Why should there be this 

 marked difference in the form and number of the nucleoli ? 1 



14. Ganglion Cells of Piscicola rapax (Verr.). 

 (Plate 23, Figs. 134-136.) 



In the ganglia of the brain occur cells of different dimen- 

 sions. Each nucleus contains most usually a single small 

 spherical nucleolus ; seldom are there two present, and in these 

 cases they are unequal in size. None of the nucleoli contain 

 vacuoles. They are excentric in position, but are never in 

 contact with the nuclear membrane. These nucleoli are small 

 in proportion to the size of the nucleus. 



15. Mtiscle Cells of Lineus gesserensts (O. F. M.). 

 (Plate 21, Figs. 51-56.) 



(The nuclei of the circular muscular layer of the body wall 

 were studied. Those of Cerebratidtis lacteiis Verr. are essen- 



1 For other observations on nucleoli in ganglion cells of molluscs, cf. the 

 reviews of the papers of Pflucke ('95), Leydig ('83). and Rohde ('96). 



