582 BULLETIN OF THE 



Compared with the first '* amphiaster de rebut," the present amphiaster is 

 characterized by the absence of vitelline rays, so prominent in the former, and 

 the presence of this granular mass of protoplasm, which is wanting in the 

 other. The axis of this amphiaster is curved, with its concavity directed to- 

 ward the formative pole. It may be that this curvature sustains some relation 

 to a vitelline protuberance which is at this moment visible at the nutritive 

 pole. The author is ignorant of the signification of this protuberance, as he 

 was of that which arises at the formation of the polar globules. 



In the following stage the groups of fibre thickenings have approached 

 closely the central corpuscle of each aster. The protuberance of the nutritive 

 pole begins to be separated from the vitellus by a circular constriction ; other- 

 wise the yolk is perfectly rounded, and shows no indication of a segmentation 

 furrow. 



This furrow makes its appearance in the next stage around the vitellus on 

 all sides ; it passes to one side of the protuberance. Biitschli's corpuscles unite, 

 on both sides, into two or three nuclei, which at once become swollen, and 

 assume the appearance of vesicles, each with an enveloping layer and embra- 

 cing irregular granules. These vesicles, some or all of them, become elongated 

 in the direction of the central corpuscle of the aster, and present an openiug 

 like the neck of a bottle, which is extended almost into contact with the cen- 

 tral corpuscle. The vesicles fuse into a single one, having the same form, thick 

 walls and a large corpuscle, which is drawn to a point on the side toward the 

 areal mass. The latter has disappeared, without doubt by absorption into 

 the nucleus, and the contents of the nucleus are in continuity with the clear 

 substance at the centre of the aster, at the expense of which the nucleus seems 

 to grow. While the segmentation is being accomplished and the new nuclei 

 are growing and taking the place of the asters, the protuberance at the vitelline 

 pole gradually disappears by fusing with that one of the spheres of which it 

 formed a part ; thus one of the products of segmentation is more voluminous 

 than the other. 



His researches on Sagitta are especially valuable, since made almost exclu- 

 sively on living eggs. They confirm the results obtained from the study of the 

 Heteropoda. The first sign of the impending division is the formation of small 

 masses of sarcode at the opposite extremities of the nucleus, which is still intact 

 and spherical. These small masses are optically like the vitelline sarcode, and 

 cause a slight indentation into the cavity of the nucleus, which, though not 

 prominent, is still readily appreciable on account of the perfect sphericity of 

 the rest of the contour. The vitelline rays tend to arrange themselves about 

 the extremities of the nucleus in place of converging towards its centre . Thus 

 is quickly produced the dumb-bell stage. The central mass of the asters is 

 perfectly homogeneous. The intranuclear trail differs frorw the surrounding 

 vitellus only by the presence of the connective striae (interzonal filaments), 

 which are pale and poorly defined. The contents of the new nuclei are clearer 

 and less refringent than their vicinage. The centre of the aster is often occupied 

 by a dark corpuscle. In the interior of the nucleus pale, ill-defined streaks of 



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