No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 29 1 



egg nucleus : " Ce nucleole a une tendance bien evidente a se 

 placer dans le voisinage immediat des noyaux folliculaires en 

 voie de formation. Le fait n'est pas constant, mais il est trop 

 frequent "; he did not actually observe that the nucleolus gives 

 off a part of its substance to the follicle cell, but supposes this 

 to be the case. 



Fol, in a second paper ('ssb) of the same year, finds that in 

 Ciona during the "production endogene " of the follicular cells 

 a segment (diverticulum) of the egg nucleus breaks off, while 

 the (then peripherally situated) nucleolus gives a part of its 

 substance into this diverticulum, and the nucleolus then wanders 

 back to another portion of the nucleus. '-'Chez Ascidia mam- 

 millata, le bourgeonnement de I'envelopjDe a lieu simultanement 

 en une fdule de points, et il est tout ou moins admissible que la 

 substance de la tache germinative dispers^e a la formation de 

 ces bourgeons." 



Gruber ('83) describes in Actinosphaeruim the growth of a 

 supposed nucleolus and its division during mitosis into two 

 equatorial plates ; though his figures would show that he 

 mistook true chromatin masses for a nucleolus. 



Jensen ('83) studied the ovum of Ciicumaria; there are from 

 fifteen to thirty nucleoli flattened against the nuclear membrane, 

 and containing vacuoles. As shown by treatment with acetic 

 or picrosulphuric acid, the outer layer of the nucleolus seems to 

 be a continuation of the nuclear membrane, so that the inner, 

 less refractive portion of the nucleolus appears to be situated in 

 a depression of the outer surface of the nuclear membrane. 



La Valette St. George ('83, quoted after Platner, '86) found in 

 the egg of an Isopod one nucleolus which is at first homogene- 

 ous, later granular, and which may enclose a vacuole and show 

 amoeboid movements. In other cases there are either several 

 smaller vacuoles or one or two larger ones. 



Leydig ('83), from comparative studies, concludes that the 

 nucleoli "sind Theile des Kernnetzes," and that each of them 

 is enclosed in a small, clear cavity of the nucleus. " Die Nucle- 

 oli konnen als eine Vielzahl von Kornchen erscheinen, die 

 unter sich gleichwerthig sind. . . . Nicht selten lasst sich bei 

 genauem Zusehen in der Menge kleiner und unter sich gleicher 



