608 GEORGE T. HARGITT 



distinguished only with difficulty. Within the nucleus is a large, 

 deeply staining nucleolus. 



In the last oogonial division there are 16 chromosomes differ- 

 ing in shape and size, but not paired either in arrangement or in 

 form and size. If conjugation of these occurs, as maturation 

 mitoses seem to indicate, the synaptic mates are unlike in some 

 cases. No contraction (synizesis) or conjugation (synapsis) 

 stages could be found, though the material was favorable in 

 character and in age. 



In growing oocytes the cytoplasm becomes vacuolated, finally 

 assuming an alveolar appearance; during growth there is a 

 passage of chromatin from the nucleus into the cytoplasm. 

 This extra-nuclear chromatin produces some vacuoles in the 

 cytoplasm as it gradually disappears. The nucleus comes to 

 have a coarse reticulum of deeply staining chromatin and, as 

 this forms, the nucleolus becomes very faintly staining. Eight 

 chromosomes (the haploid number) are formed and pass into 

 the maturation spindle, the latter being without asters or cen- 

 trosomes. Some of the chromosomes in the first maturation 

 mitosis may lag behind the others in division. The first matu- 

 ration mitosis is reductional, the second equational. The two 

 polar bodies gradually become smaller and finally disappear. 

 The chromosomes left in the egg form the egg nucleus in which 

 the chromatin is localized against the nuclear membrane. After 

 maturation the egg is liberated from the gonad and fertilization 

 takes place in the water. 



A study of the chromosomes shows that: their conjugation in 

 synapsis may take place between unlike members; the chromo- 

 somes of the oogonial divisions are not the same in form and size 

 as the chromosomes of the maturation divisions; chromosomes 

 of the maturation divisions are not exactly alike in different eggs ; 

 there is no evidence that the chromosomes of one generation are 

 descended from particular chromosomes of a previous genera- 

 tion, the contrary seems to agree more nearly with the evidence. 



The chromosomes of Aglantha are as favorable for a study 

 of chromosome behavior as many, and more favorable than 

 some, of the other phyla which have furnished material for such 

 studies. 



