Bioelow. — Nuclear Cycle of Gonionemus murbachii. 



PLATE 7. 



All figures are from entire eggs stained in borax carmine. 



Fig. 139. Fertilization. The egg nucleus is in the metaphase of the second 

 maturation division. The sperm structure consists of head and 

 middle piece, and is surrounded by astral radiations. X 500. 



Fio. 140. Fertilization. The egg nucleus is in the anaphase of the second matu- 

 ration division. The middle piece of the sperm structure has dis- 

 appeared, and the astral radiations focus at some distance from the 

 sperm nucleus. X 500. 



Fio. 141. The sperm aster has divided, and the two resultant asters lie at 

 opposite sides of the sperm nucleus. A supernumerary sperma- 

 tozoon is attached to the vitelline membrane. The egg nucleus is 

 in the anaphase of the second maturation division. X 500. 



Fig. 142. An egg showing polyspermy. Each supernumerary sperm nucleus is 

 accompanied by an aster. One sperm nucleus has joined the egg 

 nucleus, and its two asters lie on either side of the latter. X 500. 



Fig. 143. Union of the germ nuclei. The sperm asters lie in the plane of union. 

 The egg nucleus is in the reticulate " resting " condition. X 1780. 



Fig. 144. Union of the germ nuclei. The sperm nucleus, which lies in a clear 

 area, has increased in size, and become more spongy. The sperm 

 asters lie on opposite sides of the egg nucleus. X 1780. 



Fig. 145. Later stage of the same. The sperm nucleus forms a cap over part of 

 the egg nucleus, and has become less dense. X 1780. 



Fig. 140. Fusion of the germ nuclei. The sperm nucleus has broken up into a 

 large number of small chromatin masses. The egg chromatin forms 

 an irregular threadwork ; and both maternal and paternal chromatin 

 are enclosed within a single membrane. X 1780. 



Fig. 147. Later stage in fusion. The maternal and paternal chromatin form 

 threadworks which are no longer distinguishable, though the fusion 

 nucleus still has a constricted form. X 1780. 



