No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 337 



von dem Kernplasma langsam zu trennen beginnt." He could 

 not exactly determine how long the nucleolus remains in the egg 

 after that, but considers the fact important, " dass der Haupt- 

 nucleolus zur Zeit der Umbildung der Keimblaschensubstanz 

 ohne bemerkbare Volumverminderung fort besteht " ; it is at 

 this time (after the disappearance of the nuclear membrane), 

 to use his terminology, a ** Metanucleolus." 



Henneguy ('93) studied principally the genesis and occur- 

 rence of the yolk nuclei, "corps vitellin de Balbiani," in the 

 ovarian egg of various vertebrates. This body is absent in the 

 ova of the Rabbit, Bitch, Mole, RhinolopJms, Cow, Antelope, 

 Baboon ; and in Lizar'ds, Galeus, Raja, and Scylliiivi. In the 

 rat it consists of a peripheral clearer portion and a central 

 denser core ; it stains with eosin, safranin, and haematoxylin, 

 but not with methyl green or gentian violet. In the bat it 

 encloses a spherical corpuscle. It is also present in the chicken. 

 Though absent in Biifo and Triton, it is found in Rana tempo- 

 raria, where it is much the same as in birds, enclosing a more 

 deeply staining portion. In the trout the corpuscle of Balbiani is 

 as in the rat, but larger (twenty). Sygnathns : the very young 

 egg contains a nucleus " renfermant un reseau chromatique bien 

 developpe " (his Fig. 20 would show three small nucleoli enclosed 

 in this " reseau ") ; in older eggs the nuclear membrane is lined 

 by a large number of nucleoli, and " le centre du noyau est 

 occupe par une petite masse finement granuleuse et teintee en 

 rose par la safranine, tandisque le reste du contenu demeure 

 incolore. Le protoplasma ovulaire est egalement faiblement 

 colore et renferme un corpuscule arrondi, refringent comme les 

 taches germinatives et retenant la safranine avec la meme 

 intensite que ces dernieres " ; this corpuscle at the time of its 

 first appearance is flattened against the outer surface of 

 the nuclear membrane. Subsequently this intravitelline body 

 becomes elliptical in form, with its long axis parallel to the surface 

 of the egg : " il est de plus au contact immediat par son bord 

 externe avec une amas arrondi, constitue par une substance 

 fondamentale d'apparence homogene, mais remplie de granula- 

 tions tr^s colordes. A un stade plus avance tout le corps 

 refringent s'est transform^ en un amas let qu'on I'observe dans 



