Bioelow. — Nuclear Cycle of Gonionemus murbachii. 



PLATE 8. 



All figures are from entire eggs stained in borax carmine. 



Fig. 148. Union of the germ nuclei by apposition. In the egg nucleus the chro- 

 matin forms a threadwork ; in the sperm nucleus it consists of many 

 small masses connected with one another by linin strands. X 1780. 



Fig. 149. Union of the germ nuclei by apposition. The two nuclei are of nearly 

 equal sizes and are both in the reticulate resting condition. X 1780. 



Fig. 150. First cleavage nucleus formed by the fusion of the germ nuclei. The 

 chromatin forms an irregular threadwork, in which the maternal and 

 paternal components are not distinguishable. X 2600. 



Fig. 151. Prophase of first cleavage. The nuclear membrane has broken down, 

 and the chromatin forms separate segments. X 2600. 



Fig. 152. Late prophase of first cleavage. There are twenty-four chromosomes 

 formed by the condensation of the chromatin segments. Maternal 

 and paternal groups are not distinguishable. X 2600. 



Fig. 153. Metaphase of first cleavage spindle. The chromosomes are in the full 

 somatic number. The asters are small. X 1780. 



Fig. 154. Oblique polar view of daughter plate of first cleavage, showing the full 

 somatic number of chromosomes. X 2600. 



Fig. 155. Metaphase of second cleavage. The chromosomes are in a reduced 

 number. The asters are small. X 1780. 



Fig. 156. Anaphase of second cleavage. The asters are much larger, and the 

 daughter chromosome groups form minor centres of radiation. 

 X 1780. 



Fig. 157. Polar view of daughter chromosome group of second cleavage. There 

 are twelve bivalent chromosomes, several of which show their double 

 nature by their constricted outlines. X 2600. 



Fig. 158. Polar view of daughter chromosome group of second cleavage. There 

 are nine chromosomes which are clearly bivalent ; the remaining five 

 are probably univalent. X 2600. 



Fig. 159. Side view of fourth cleavage spindle in the metaphase. The chromo- 

 somes are present in the full somatic number. X 1780. 



Fig. 160. Polar view of daughter chromosome group of fourth cleavage. 

 There are twenty-four chromosomes. X 2600. 



