MUSEUM OF COMPARATIVE ZOOLOGY. 429 



Stossich seems to have made, with some other observers, the mistake 

 of confounding the astral areas with new nuclei. 



FoL (76, pp. Ill - 113, 138 - 145, PI. IV. Fig. 3) describes, but does 

 not very fully illustrate, the phenomena of maturation in the Hetero- 

 pods. " The nucleus had already disappeared in all the eggs (Firo- 

 loides) which I have observed, to reappear before and after the escape 

 of the corpuscules, de rebut." This statement, with some parts of the 

 immediately following description, is certainly unique. Perhaps the 

 account may be the result of a faulty combination of observations. 



Fol gives for Pterotrachea the details of the changes, of which the 

 above quotation is an epitome, as follows. The molecular star has the 

 same appearance as in Pteropods. There is, however, this difference, 

 that the protoplasm is so scanty as to form only a thin layer between 

 the nucleus"^ and the "protolecithe." When the nucleus [germinative 

 vesicle 1] has vanished, the vitellus appears composed merely of two very 

 clearly marked spheres set concentrically one within the other. The 

 sphere within is nothing else than the protoplasm, the greatest part, 

 but not the whole, of which surrounds itself with a membrane^ and be- 

 comes a central nucleus. At opposite (nutritive and formative) poles of 

 this nucleus there soon appear two centres of attraction whence proto- 

 plasmic rays emerge in all directions [first archiamphiaster]. The 

 stouter of these striations stretch from one centre to the other in the 

 interior of the nucleus. The limits of the latter disappear and the 

 stars move apart. Biitschli's fusiform body is only the central part of 

 the vanished nucleus. As to the fibres of the spindle, they are only 

 striations in the protoplasm. One of the stars approaches the centre, 

 the other nears one pole of the vitellus and there gives rise to the first 

 polar globule. In the interior of the globule is readily to be distin- 

 guished the termination of the spindle fibres (Biitschli), which have 

 their centre at the middle of the exterior extremity of the globule. 

 There enlargements of these striae are also to be observed. The star 

 in the vitellus now divides anew, without having taken the form of a 

 nucleus. During this division the striations, arranged in the spindle 

 form, reappear. Then the second globule is formed, in the same man- 



* It is often^ difficult to comprehend Fol's meaning because he uses the terra 

 " nucleus " in the most general sense, when accuracy demands a more explicit term. 

 Here, for example, he speaks of the existence of a nucleus where, to judge from what 

 has preceded (Firoloides and Pteropoda), one has the right to suppose that the 

 germinative vesicle has been supplanted by a molecular star, and that consequently 

 there is no nucleus. 



