312 Elliot R. Downing, 



it is only toward the close of its growth that it becomes actively 

 amoeboid (Fig. 7, Plate 11). The butterfly shape so long- characteristic 

 to the egg of H. viridis is absent in H. dioecia. When growth is 

 complete, sufficient yolk having been formed, the pseudopodia are 

 withdrawn and the e,^g becomes biscuit shaped. But it is again 

 spherical while the polar bodies are being formed. Then it becomes 

 more irregular again in the interval before it bursts out of the 

 restraining ectodermal sheath. During this process of outflow it 

 seems a giant amoeba with retracted pseudopodia and the form is 

 ever changing. Finally the shape is spherical except for the stalk 

 of protoplasm which attaches the egg to the ectoderm. The base 

 of this stalk is expanded and this foot is held in the contracted 

 ectodermal cavity previously occupied by the ^gg. In H. viridis 

 and H. fusca this stalk is narrow and deeply imbedded; in H. dioecia 

 it is broad and is attached by a broad, sucker-like disc, the ecto- 

 dermal depression being slight (Fig. 1, Plate 11). There is at the 

 pole opposite the stalk, the animal pole, a depression by means of 

 which the sperm enters; this depression does not invariably occur 

 opposite the attaching stalk; I have found it ninety degrees from 

 this point. 



16. Contemporaneously with the change in the shape and size 

 of the Qgg the nucleus is changing its size and structure; it appears 

 large in proportion to the cell body, at first. The primitive oogonia 

 have a length of about 10 /< with a slightly less breadth: the 

 nucleus is some 8 /< in diameter and contains a prominent nucleolus 

 (see Fig. 4, Plate 11). The nucleus grows as the Qgg grows until it 

 attains a maximum size, just before maturation in H. dioecia. of 

 60X45 (.1 (Fig. 8, Plate 11). The nucleolus has also grown by fusing 

 with smaller nucleoli that form freely (Fig. 9, Plate 11). The reticulate 

 structure of the nucleus is, at first, coarse but it becomes finer and 

 finally almost completely disappears, the protoplasm seeming finely 

 granular. The changes immediately preceding maturation will be 

 discussed below. 



17. While the tgg is yet small, there appear, in H. viridis, gra- 

 nules scattered through its substance which Kleinenberg thinks are 

 equivalent to the white of the ^.gg in the higher forms; these later 

 disappear and the green bodies, now known to be algae, begin to be 

 manifest, Protagon granules are not found in the ^gg of H. dioecia 

 or of H. fusca and of course no algae are present. 



18. The pseudozellen originate in two ways : 1. by the confluence 



