Manchester Memoirs, Vol. Ixii. (191 7), No. 2 25 



but not until after the fusion of the male and female nucleus. 

 Thus we have the extraordinary phenomenon of fertilisation pre- 

 ceding maturation. Shearer was unable to obtain a detailed 

 acoount of maturation of the eggs, but there appears to be twenty 

 somatic chromosomes in both male and female. Two polar 

 bodies are given off by both types of eggs, and in each case 

 twenty chromosomes are extruded and twenty remain in the egg. 

 What occurs in the formation of thei second polar body of the 

 female egg is not known, but in the male egg ten double chromo- 

 somes are again extruded, leaving ten double ones in the egg. 



As Shearer remarks, the two most remarkable results of this 

 work are the way in which fertilisation occurs, and maturation 

 occurring after fertilisation. The maturation divisions are also 

 very puzzling, and cannot be satisfactorily explained. The whole 

 difficulty is so admirably expressed by Shearer that I cannot 

 do better than quote his own words : " With regard to matura- 

 tion divisions, I aim forced to admit that their evidence is very 

 puzzling, and I am quite unable to explain them at present. 

 In the case of the male egg, We should expect, as this has not 

 been fertilised, and is therefore! in a sense developing partheno- 

 genetically, it should agree with the development of the male 

 parthenogenetic egg of Rotifers, and other forms, where they 

 develop in the " n " condition, where " n " represents the reduced 

 number of chromosomes. This is certainly not the case in 

 Dinophilus, where the male egg, after reduction (if any reduction 

 takes place), possesses apparently the full 2n number. It is, 

 however, possible that the male egg of Dinophilus is similar 

 to that of the Phylloxerans, which develops in the 2n — 1 or — 2 

 condition, as it is difficult accurately to count the chromosomes 

 in the segmentation divisions of the male egg On account of their 

 small size. In the female e.gg we should expect them, since they 

 have been fertilised before reduction, to be in the 2n+n condition 

 if we consider the sperm 'to bring in the n number. In the first 

 maturation division of the egg we should expect to find at least 

 thirty chromosomes, whereas their number is somewhere about 

 twenty. On the other hand, if we suppose the female germ cells 

 to be in the " n" condition when they appear in the ovary, then 

 after fertilisation they should show the 2n number of chromo- 

 somes, which agrees with the facts, but 'does not explain how the 

 male egg, which has not been fertilised, is nevertheless in the 

 2n — 1 or — 2 condition. Therefore, from whatever point of view 

 we choose to regard if, there is no way of bringing the facts of 

 maturation divisions into line at present."* 



* The question of sex production and the early differentiation, during develop 

 ment, of germ cells from somatic cells has been ably discussed by Hegner in a long 

 series of papers. The whole matter is summarised in his book " The Germ -Cell 

 Cycle in Animals." New York, 1914. 



