94 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
mungsprodukten neue solche Partien. Die eigentliche Furchungshóhle 
tritt bei Cyclas, wie wir schen werden, erst in bedeutend höheren 
Furchunesstadien 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- 
cossively 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 tho 
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, mi, m?, m?, mi, 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 Lovén (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 
allen den Fällen, wo ein nachträgliches Abflachen der kleineren Zellen 
konstatiert wurde, auf günstigen Prepäraten auch der helle Raum 
zwischen den Furchungskugeln hätte nachgewiesen worden können, der 
durch sein Verschwindung das Anschmiegen der Mikromeren möglicher- 
weise bedingt." “Der helle Raum ” has, however, never been recorded 
by any investigator of these forms; furthermore, the fusion in some 
sases (and these are the most marked cases of fusion) consists in the 
reunion of the more richly protoplasmie 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 
* maeromere?' 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 inferenco that it is essentially of 
that nature in the later stages. Stauffacher himself does not emphasize, 
