HARGITT: PENNARIA TIARELLA AND TUBULARIA CROCEA. 179 
Polyspermy is of frequent occurrence. ‘The sperm head begins its 
transformation into the sperm nucleus soon after entrance, and while 
close to the surface of the egg. ‘The egg nucleus is often composed of 
several distinct vesicles, and the sperm nucleus occasionally appears 
lobed, as though formed by the confluence of several vesicles. An 
aster may accompany the sperm nucleus, or it may perhaps be in 
connection with the egg nucleus, but at the time of apposition of the 
nuclei no astral radiations are present, as a rule. A complete fusion 
of the nuclei may occur, or they may retain their independence while 
the first cleavage spindle is forming. Chromosomes seem to take 
their definitive form only after the first cleavage spindle is present. 
The origin of the cleavage asters could not be determined. 
4. Cleavage.— Figure 27, which shows the first-cleavage spindle 
forming, gives the impression of its formation from the cytoplasm, 
since the nuclear membrane, still intact, is deeply indented opposite 
the aster, the astral rays extending into the indentations. ‘The second 
cleavage spindle (Fig. 28) gives evidence of the same thing, for although 
the spindle fibres are nearly formed, and the elongated nucleus is in 
the axis of the spindle, the nuclear membrane is still unbroken. Large 
conspicuous asters occur at the poles of the second cleavage spindle; 
the radiations do not enter the large clear centrosphere, nor is there a 
central body found in it. The chromatin of the nucleus is beginning 
to produce beaded strands, though definitive chromosomes are not yet 
formed, and a part of the reticulum remains. In this egg, although 
the second spindle is forming, the first cleavage furrow is only started, 
and in other eggs when the third division of the nucleus had begun 
the first cytoplasmic division was still unfinished, and the second 
cleavage furrow only just started. This delay in the cytoplasmic 
division was found by Hargitt (:04°) to be common in Pennaria, and 
we shall see that it is also typical in Tubularia. Further cleavage 
stages of Pennaria have not been studied. 
B. 'TuBULARIA CROCEA. 
1. Oégonia.—'The primordial germ cells divide mitotically to 
form the odgonia, which are so closely packed around the spadix that 
their outlines are obscured, if not wholly obliterated, as has been de- 
scribed by Allen (:00). The nuclei of the odgonia are relatively large 
and each contains a single large nucleolus, as Allen has also observed. 
The nucleolus stains intensely in iron hematoxylin, but in hematoxylin 
and eosin it selects the acid or plasma stain. Delicate linin fibres 
