MUSEUM OF COMPARATIVE ZOOLOGY. 581 



and its membranes is better preserved than in picric acid. The vitellus as a 

 whole still continues flattened, and the same peculiarity affects the "areas" 

 and the contained globules. The bodies of the centre of the aster appear small 

 and homogeneous. At first located in the centre, they subsequently approach 

 the young nuclei, with which they ultimately unite. Certain pale corpuscles 

 between the first and second membranes are not polar globules, but result 

 from a precipitate formed in the albuminous fluid by the reagents. The 

 descriptions and figures of the corpuscles which occupy the centre of the aster 

 do not seem to "me to afford satisfactory proof of the conclusion, that they are 

 fused with the new nuclei. Figs. 13, 14, of Fol's PI, VI. show thickenings in 

 the interzonal filaments. 



In describing the formation of the polar globules in the Heteropoda, Fol 

 expresses his belief that all the " matieres de rebut " eliminated from the egg 

 correspond to a single cellular element. Here, too, the female pronucleus is 

 formed by a fusion of the central corpuscle of the deep aster with the compact 

 corpuscle formed at the expense of the "renflements de Biitschli." As he has 

 seen only one such corpuscle result from the enlargements, he thinks there is 

 every reason to believe that the supplementary small nuclei (which he finds 

 here) are formed, as in Asterias, independently of the first pronucleus in the 

 substance of the central mass of the internal aster. 



The first segmentation in the Heteropoda is as follows. The pronuclei be- 

 come mutually flattened, the enveloping layer disappears from the surface of 

 contact. This region of contact is the centre of an irregular system of diver- 

 ging rays extending inside as well as outside the nuclei. This might be 

 mistaken, he says, for the origin of the amphiaster ; but by comparisons 

 he has convinced himself that these first radial striae correspond only to 

 the molecular activity which is developed at the moment of the fusion of 

 the nuclei, and that it disappears before the amphiaster arises. However it 

 may be with the Heteropoda, I believe it is not thus with Limax. According 

 to the further description, the plane of union is still visible in Heteropoda 

 after the stars of the amphiaster have appeared. The latter always fall at 

 opposite margins of that plane. At other times the fusion is more complete 

 when the asters arise. The pronuclei meanwhile migrate nearly to the centre 

 of the yolk. The contours of the (conjugated) nucleus remain visible up to the 

 moment when the intranuclear enlargements are grouped in the vicinity of 

 the centre of each aster. The middle region of the " filaments connectifs " 

 (PL IX. Figs. 8, 9, 10, Ft) is composed of fine fibrillse, which, the author 

 states, have been incorrectly engraved, so that they appear like thickenings of 

 the filaments. The spaces around the centres of the asters are occupied by 

 granular protoplasm exhibiting a radial structure. Perhaps they correspond, 

 he says, to the sarcodic masses which occupy the same position in the sea- 

 urchin. The vitelline filaments of the latter would then correspond to the 

 radial trails of protoplasm which stretch out between the lecithic globules of 

 Pterotrachea. In that event equivalents of the rays immediately around the 

 centre of the aster in the mollusks would not exist in the sea-urchin, or would 

 be invisible by reason of the homogeneous nature of the sarcodic mass. 



