402 BULLETIN OF THE 



sion during this period of migration in the irregular changes of form 

 which the outline of the yolk undergoes. 



Assuming that in Auerbach's observations the female pronucleus is the 

 one making its appearance at the small end of the egg, an occasional 

 variation from the normal method is observable ; for this (female 1) pro- 

 nucleus sometimes begins its migration before the male, and therefore 

 meets it between the centre and the blunter pole of the egg. Another 

 variation consists in the occasionally observed origin of the pronuclei at 

 some distance from either pole, in this case, however, usually at diametri- 

 cally opposite points of the surface. 



The further history of the female pronucleus will be considered under 

 the head of Fecundation. 



Van Bambeke (76, p. 4) has observed that in unfecundated eggs of 

 Tinea vulgaris a spherical portion is sometimes detached during the 

 active changes of form which the germ undergoes, and questions if these 

 are polar globules. 



The fecundated Pteropod egg, according to Fol (75, p. 196), is desti- 

 tute of both membrane and nucleus. It is composed of two parts, for- 

 mative and nutritive, the latter being a network of protoplasm in whose 

 meshes are found nutritive globules. At the centre of the formative part 

 there is a star formed by granules of protoplasm arranged in straight di- 

 vergent lines which extend as far as the limit of the formative part ; the 

 nutritive globules also arrange themselves in lines. After the escape of 

 the polar globules a nucleus appears at the centre (au centre) of the star. 

 The latter disappears in proportion to the increase in the size of the nu- 

 cleus ; and the granules and globules cease to be in line. 



In his second paper on the development of Anodonta, Flemming (75, 

 pp. 109 — 118) makes some additions to his previous communications on 

 the earliest changes of the egg. The clear spot in the yolk, although 

 less distinct, is visible after the elimination of the polar bodies is com- 

 pleted ; it therefore cannot have corresponded to the second polar globule 

 alone. The latter, at first naked, possesses, after a variable length of 

 time, a membrane. The appearance within it of a large, usually rough, 

 angular, and highly refractive corpuscle, generally attached somewhere 

 to the membrane, is probably a symptom of the death of the globules. 

 The corpuscle and membrane stain more intensely than the contents, 

 " so that one is reminded of a small cell with nucleus, or a nucleus with 

 nucleolus. It would of course in the diagnosis be premature to decide 

 by such a similarity." The polar globules are found to persist, in a 

 shrivelled condition, much longer than was at first supposed. 



