hargitt: pennaria tiarella and tubularia crocea. 187 



in a different place and manner, no stages having been obtained con- 

 necting this with the maturation spindle. In Tubularia, the oocytes 

 not used as food often remain in contact with the egg, and when de- 

 generating they bear so close a resemblance to polar cells as to make it 

 almost impossible to distinguish between the two, unless the polar cells 

 are still actually joined to the egg. However, what little evidence 

 there is favors the view that this nuclear condition in Tubularia is a 

 stage immediately preceding the formation of the first polar cell. A 

 fragmentation of the nucleus at or before this time, as claimed by 

 Allen (:00), does not occur, the polar cells being formed without doubt 

 by mitosis. There is no case in which I have not been able to find a 

 nucleus of some sort in each egg examined, and never has there been 

 the slightest sign of fragmentation. A spindle found close to the sur- 

 face of the egg in a nearly radial position (Fig. ola) may represent the 

 first maturation spindle. Centrosomes and asters could not be de- 

 tected. ^Yhile the preservation of this egg was not perfect, it was 

 good enough to show the structure of the spindle itself clearly. The 

 chromosomes in the ecjuatorial plane, while very small and massed 

 together, show a splitting, and the two parts are just beginning to 

 separate. The small sphere outside the egg, at the left of the figure, 

 may represent a polar cell, but in size and general appearance it is 

 more like a degenerate oocyte. In the centre of this egg was found 

 another nuclear body (Fig. 51b), which probably represents the sperm 

 nucleus. The second maturation spindle was not seen in Tubularia. 



Figure 52 shows the two polar cells, one of which is still joined to the 

 egg by interzonal filaments (the body shown with dotted outlines was in 

 the section following the one drawn with a continuous outline). The 

 two polar cells are equal in size, each contains some cytoplasm, and the 

 chromatin is in several masses not surrounded by a membrane. The 

 egg nucleus has the form of a single spheroidal vesicle with the chro- 

 matin scattered along a reticulum; no asters were present. Figure 

 53 shows a nearly tangential section of another egg, provided with two 

 polar cells outside the membrane. In this case, too, the chromosomes 

 are aggregated into several discrete masses. The egg nucleus occupies 

 a superficial position in an elevation of the surface of the egg, and there 

 are no cytoplasmic radiations in its vicinity. 



In one case only (Fig. 54) was a spermatozoon found within the egg. 

 The sperm head had as yet undergone no marked change. It was 

 accompanied by a distinct aster, in which, however, no centrosome 

 could be detected, though several stains were used in an attempt to 

 demonstrate one. Unfortunately the condition of the egg nucleus 



