1901.] NATURAL SCIENCES OF PIIILADELI'IIIA. 715 



cell syncytium. The smallest separate egg cells, O.,, are rather 

 square, having as yet no stalk. The cytoplasm is clear and slightly 

 granular, with no yolk granules, and there is a delicate cell mem- 

 brane. The nucleus is round, about .0058 mm. in diameter; a 

 small nucleolus is present, but no chromatin is demonstrable, proba- 

 bly on account of admixture with plastin, and the whole nucleus 

 takes a plasma stain, pink with hsematoxylin-eosin. 



In the next stage, the young ovum, 0..,, has lengthened, the 

 distal end is somewhat rounded and the proximal end more 

 slender, so that the whole cell is now pear-shaped. The proximal 

 end constricts more and more until it becomes a slender stalk, by 

 which the rounded distal end or cell body remains attached to the 

 gonad w'all. The nucleus has enlarged, measuring about .023 mm. 

 in diameter, likewise the nucleolus, in which scattered vacuoles are 

 forraiug. Yolk granules are beginning to appear in the cytoplasm. 



After the appearance of the yolk the cytoplasm has quite a 

 difierent look, being denser with the fine yolk granules scattered 

 throughout. The nucleus of this stage, O.3, is much larger, .035 

 mm. The nucleolus has not increased much in size, but the small 

 scattered vacuoles have fused into one large disk-shaped vacuole, 

 n.vac, at the periphery of the nucleolus. 



The ovum is now surrounded by two egg membranes, the outer 

 of which, o.O.mh., is considerably thicker than the inner and 

 stains blue, while the inner takes a faint pink, ha3matoxylin-eosin 

 stain. The formation of the egg membranes has not been fol- 

 lowed with any exactness, but I believe that both membranes are 

 formed by the egg. Bohmig (1898) believes this is the case in 

 Stichostemma gravense. Montgomery (lo95) states that in S. 

 eilhardl only the inner egg membrane is a " yolk membrane," the 

 outer being derived from the germinal epithelium and is therefore 

 a true chorion. 



The oldest stage found, figs. 25, 52, is that of a free ovum iu 

 the centre of the gonad, no longer attached to the wall by its 

 stalk. Both membranes are present, the outer one, fig. 52, 

 0. O.mb., being often broken and discontinuous, as if it were about 

 to be sloughed off. This appearance, however, may be an artifact, 

 as the specimen from which it is drawn was badly shrunken. At 

 this stage the gonad contains twenty or more ova of equal size, in 

 such close contact with each other that they assume a polygonal 



