94 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



mungsprodukten neue solche Partien. Die eigentliche Furchungshohle 

 tritt bei Cyclas, wie wir sehen werden, erst in bedeuteud hoheren 

 Furchungsstadien auf." 



A cavity similar to that of the two-cell stage is figured for the four-, 

 five-, six-, seven-, nine-, and twelve-cell stages, occurring always between 

 the macromere and its most recent products. This cavity becomes suc- 

 cessively smaller from the four- or five-cell stage until we reach the 

 relatively small cavity of the twelve-cell stage. It is always sharply 

 limited from the macromere, and often presents on the side next the 

 most recent micromere, or its products, the gradual merging into the 

 granular protoplasm noted in the two-cell stage. That is to say, here, 

 as there, the inference is that the cavity may be regarded as an intra- 

 cellular space. The fluid which fills this decreasing cavity he thinks is 

 absorbed in large part by the macromere, and perhaps to a less extent 

 by the micromeres, and that it does not pass out of the cavity through 

 the egg membrane. After this fluid-filled space has disappeared from 

 between the earlier formed micromeres, m 1 , ni 2 , m 3 , m 4 , and the macro- 

 mere, the micromeres in question apply themselves closely to the 

 macromere in a way that suggests the fusion of micromeres with the 

 macromere noted, as by Loven ('49) in marine Lamellibranchs, and by 

 Bobretsky ('77) in Nassa. With regard to the interesting phenomenon 

 of fusion described by these authors, Stauffacher makes the following 

 suggestion : " Es erscheint mir nicht unwahrscheinlich dass vielleicht in 

 alien den Fallen, wo ein nachtragliches Abflachen der kleineren Zellen 

 konstatiert wurde, auf gunstigen Preparaten auch der helle Raum 

 zwischen den Furchungskugeln hatte nachgewiesen worden kbnnen, der 

 durch sein Verschwindung das Anschmiegen der Mikromeren moglicher- 

 weise bedingt." " Der helle Raum " has, however, never been recorded 

 by any investigator of these forms ; furthermore, the fusion in some 

 cases (and these are the most marked cases of fusion) consists in the 

 reunion of the more richly protoplasmic part of the macromere with 

 the more passive yolk-bearing portion, from which it had abstricted 

 itself at the time of nuclear division. 



Neither Bobretsky ('77) nor Brooks ('80) figures a nucleus in the 

 " macromere " with which the micromere so completely fuses ; and it 

 seems hardly possible that in these cases the disappearance of a cavity 

 can have anything at all to do with the phenomenon of fusion. There 

 are moreover some objections to the view that in the two-cell stage the 

 cavity lies within the cell, and to the inference that it is essentially of 

 that nature in the later stages. Stauffacher himself does not emphasize, 



