198 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ever been seen. ‘The supposed disappearance of the germinative 
vesicle at this time, I believe to be due simply to the usual dissolution 
of the nuclear membrane and the mingling of karyoplasm with cyto- 
plasm which is characteristic of the prophase of mitosis. After this 
dissolution of the nuclear membrane maturation spindles are formed, 
two polar cells are constricted off from the egg, and the chromosomes 
remaining in the egg form a definite vesicular egg nucleus. 
4. Nucleolus.—'The nucleolus of odcytes of Hydromedusae has 
been described as plasmatic and not aiding in the formation of chromo- 
somes by Brauer (’91°), Hacker (’92), Morganstern (:01), Wulfert 
(:02), Harm (:02), Trinci (:07), Miiller (:08), and Conklin (:08). 
Trinci (:05) finds in the Eucopidae that the nucleolus divides into pieces, 
some of which are chromatic and resemble ‘‘pseudo-nucleoli’’ of 
Amphibia; in Phialidium the same author (:07) describes a chief 
nucleolus, with acid and basic constituents, not aiding in the formation 
of chromosomes, and smaller chromatic nucleoli, which help to form 
chromosomes. Stschelkanowzew (:06) maintains that in Cunina the 
chief nucleolus alone, which is chromatic, forms the chromosomes, 
though small plasmatic nucleoli are also present. Bigelow (:07) 
describes the chief nucleolus in Gonionemus as staining like chromatin, 
but it takes no part in chromosome formation and is considered as a 
by-product; accessory nucleoli which occur are plasmatic bodies. ‘The 
nucleoli which do not form chromosomes are either (1) cast into the 
cytoplasm, where they are dissolved,— Brauer (91°) "Tubularia 
mesembryanthemum, (’91*) Hydra (in part), Hacker (’92) Aequorea, 
Morganstern (:01) Cordylophora, Harm (:02) Clava, Hargitt (:04*) 
Pachycordyle, (:06) Clava, Trinci (:07) ‘Tiarella,— or (2) fragmenta- 
tion occurs and the pieces are for the most part dissolved in the nucleus 
— Brauer (’91*) Hydra (in part), Wulfert (:02) Gonothyraea, Trinci 
(:05) Eucopidae (in part), (:07) Phialidium, Miller (:08) Cladonem- 
idae and Codonidae. 
In Pennaria and Tubularia crocea the nucleolus is entirely plasmatic 
in all o6gonia and odcytes. In Pennaria it seems gradually to dissolve 
in the germinative vesicle, without fragmenting. In Tubularia it may 
lose some of its substance in liquid form, or in fragments, at an early 
and variable stage in the growth of the odcyte; but eventually the 
remainder fragments into few or many parts. Of these, some may 
dissolve in the nuclear sap; others are added to the nuclear reticulum 
and are apparently transformed into chromatin. ‘The complete dis- 
appearance of the nucleolus within the germinative vesicle before the 
dissolution of the nuclear membrane, and before the chromosomes are 
f x3 
— to See gy a eer pee ae oy es 
