188 . BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
could not be determined. ‘The only evidence of such a body was an 
aster in the cytoplasm not far from the spermatozo6n and near bodies 
which, though staining rather faintly, appeared to be chromatic. 
Their condition and arrangement could not be made out with sufficient 
clearness to determine whether or not they were definitive chromo- 
‘ somes. ‘lhe surface of the egg was elevated at this point, and it may 
be that a polar cell was about to have been formed. In the vesicular 
sperm nucleus represented in Figure 51b, the chromatin is scattered in 
granules through the reticulum. No asters or radiations of any sort 
accompanied it. At the surface of the egg there still remained a small 
cone, but between it and the sperm nucleus there was no “path” in 
the cytoplasm. Since this egg had a maturation spindle, it seems 
probable that the spermatozo6n may enter before the polar cells are 
formed. No further stages in fertilization were found, the next more 
advanced stage observed being that of the first cleavage spindle in 
metakinesis. 
4. Cleavage.— Segmentation is total but unequal, and it is often 
irregular in its progress. ‘There is no localization of yolk material to 
account for this irregularity, which may possibly be due in part to the 
fact that development takes place in a closed gonophore; but this will 
not wholly explain the irregularity, for the segmentation of Pennaria 
tiarella as described by Hargitt (:00, :04°) is strikingly irregular, and 
yet this egg develops free in the water. Colonies of Tubularia crocea 
collected from different localities, or from the same place at different 
seasons, show in some cases quite regular cleavages; other lots are 
almost as constantly very irregular. Whether there is any significance 
in the fact that colonies collected in the fall were more regular in cleav- 
age than those collected from the same point in the spring, I do not 
know; but this difference becomes evident upon comparing series of 
sections of two such lots. It may be stated as a further general con- 
clusion, supported by all the eggs examined, that cleavage is always 
accomplished by mitosis. This is especially evident in the early stages, 
just where Allen (:00) claims to have found indications of the reorgan- 
ization of a previously fragmented nucleus. It was because of this 
contention of Allen that especial care was taken to examine closely 
the early cleavages, and in no instance was there any indication what- 
ever that a reorganization of fragmented particles was occurring. 
Furthermore, all cleavages up to the end of segmentation showed no 
sign of amitotic division, it being possible in almost every case to de- 
termine the line of descent of each nucleus through preceding mitoses. 
A certain polarity is shown by the egg, though its poles are quite 
yea 
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