GAMBTOGENESIS AND FERTILISATION IN NEMATUS RIBESII. Ill 



day the polai* mitoses are abnormal. The most extreme 

 case (fig. 23) shows the " polar protoplasm," full of dots 

 arranged roughly in lines like irou-filings in a magnetic field. 

 At each pole of the figure is a group of more conspicuous 

 stained bodies which may be chromosomes. Some of the 

 other eggs show a somewhat similar appearance on a smaller 

 scale, and in others nothing is clearly distinguishable in the 

 polar protoplasm. In all the eggs the peripheral protoplasm 

 is narrower than usual, and in the most markedly abnormal 

 eggs it is practically absent. I have occasionally found 

 appearances of the same kind, but much less pronounced, 

 in eggs laid by other insects, but have not sufficient cases to 

 be able to throw any light on their meaning.] 



Summary. 



1. True fertilisation (conjugation of male and female 

 pronuclei) may take place in N. ribesii, and the behaviour 

 of the polar nuclei is slightly different in fertilised and virgin 

 eggs. 



2. In the spermatogenesis there are eight chromosomes in 

 spermatogonia! divisions; four ^'gemiui" appear at the 

 beginning of the maiotic phase, and by heterotype and homo- 

 type mitoses distribute four chromosomes to each spermatid. 



3. In the oogenesis eight chromosomes appear in oogonial 

 mitoses, but in divisions of nuclei in the ovary sheath more 

 than eight are found, suggesting that the chromosomes of 

 the germ-cells are compound. 



4. In the polar mitoses of the egg two types of maturation 

 are found. In some eggs there are successive equation 

 divisions so that the egg nucleus and each of the three polar 

 nuclei contains eight chromosomes. In other eggs normal 

 reduction takes place, separating entire chromosomes from 

 one another, and only four are found in each of the daughter 

 nuclei. 



5. It is probable that only such reduced eggs are capable 



