MUSEUM OF COMPARATIVE ZOOLOGY. 583 



protoplasm are seen, which together resemble the tongue of a bell, and are 

 joined with the central substance of the aster. During the second and subse- 

 quent segmentations these streaks of sarcode become at a certain moment much 

 more distinct than during the first segmentation ; they take special forms, 

 which recall the stamens of a flower. There are from four to six of them, but 

 their position is not constant. They attain their greatest distinctness only 

 when the nuclei are so swollen as to be perfectly spherical. Although a mor- 

 phological continuity of these trails (trainees) with the enlargements of the bi- 

 polar filaments appears improbable, it is not absolutely impossible. One might 

 suppose that only a part of the enlargements serve to form the envelope of the 

 young nuclei, and that another part persists under its primitive form [the 

 trails] to become subsequently the intranuclear network. Whatever their ori- 

 gin, these trails of protoplasm disappear during the growth of the new nuclei, 

 and contribute without doubt to the formation of the sarcodic network. The 

 nucleoli make their appearance only a long time after the disappearance of these 

 trails, so that they do not seem to have any direct relation with them. 



The author arrives at the following conclusions concerning the process of 

 segmentation in general. 



The first precursory phenomenon is the appearance of a stellate figure, — 

 a radial arrangement of the vitellus, of which the nucleus is the centre. At 

 this moment the nucleus is still intact, but a little less distinct than before ; 

 this appears to indicate that there are movements, — forces which exert their 

 influence at the same time upon the nucleus and upon the vitelline protoplasm. 

 The refringency of the nucleus and the distinctness of its contours are the only 

 things which are modified, up to the moment when the new centres of attrac- 

 tion appear at its opposite poles. The nature of these forces are far from being 

 elucidated, but there are in all cases places where a gradual passage is estab- 

 lished between the nuclear substance and the vitelline protoplasm ; there are 

 therefore points of fusion between the two substances. These centres persist a 

 certain time under the form of corpuscles or of granular masses. The rays of 

 the amphiaster appear at first in immediate contact with the centres, and then 

 stretch out in all directions. They fall into two categories, according as they 

 extend into the interior of the nucleus or into the vitellus. The former are the 

 only ones that are joined end to end. Both kinds bear enlargements ; but 

 those of the extranuclear filaments have no other destination than to add their 

 mass to that of the centre of the aster, while the intranuclear unite in the 

 vicinity of the centre of each aster into one or a small number of corpuscles, 

 which become swollen and unite into a single vesicle, and thus become the 

 origin of the new nuclei. The corpuscles occupying the centre of the star 

 also contribute to the formation of the nuclear elements, which continue to 

 grow at the expense of the sarcodic masses of the asters. The " filaments con- 

 nectifs" remain outside the new nuclei, and do not contribute to their forma- 

 tion. The new nuclei therefore absorb only a part of the substance of the old 

 nucleus, and in return are united with substances which formerly constituted 

 a part of the vitellus. The formation of the polar globules takes place by the 



