IN THE OOCYTES OF THE GALL-FLY NEUROTERUS. 329 



hypoderm itself I noted the occurrence of 30 chromosomes at each pole. In 

 one case this number (30) was quite unmistakable. In three nuclear divisions 

 in the same region the haploid number occurred ; and it is perhaps of some 

 significance that the two numbers are complementary. It is thus possible 

 that the occurrence of the haploid figure may be due to a difference of 

 polarity — pathological maybe — in the dividing nuclei. 



The Development of the Oocyte. 



As there are two kinds of ova produced by the agamic generation in 

 N. lenticalaris (viz. those which undergo maturation and give rise to males, 

 and others which do not form polar bodies and are female producing), it 

 appeared possible that differences might occur in different individuals durino- 

 the synapsis stages. No points of contrast between the very young oocytes 

 of different agamic females could be detected either in Neuroterus le?iticularis 

 or in iV. numismatis, although the ovarioles of more than twenty individuals 

 were examined. 



Synapsis occurs in the upper part of egg-tubes of ovaries in which the 

 former have just become differentiated. The cells of this region are 

 arranged in groups of about 8 to 16, and synizesis nuclei can be seen before 

 it is possible to distinguish nurse-cells from oocytes. Subsequently the 

 chromatin material of certain cells, which are to become nurse-cells, under- 

 goes fragmentation into very numerous granules. Their nuclei later exhibit 

 one or two large karyosomes of irregular shape : these at a late staore 

 disintegrate and are ejected into the cytoplasm. During the growth period 

 it is not possible to detect definite chromosomes in the oocyte nucleus, 

 the chromatin content of which greatly loses its staining capacity. One or 

 two karyosomes and a plasmosome are found often lying on the outer side of 

 the nucleus. As in Andricus, there is no oosoma at the posterior end of the 

 egg like that described by Hegner in Diastrophus or the body referred to by 

 Weissmann in Rhodites. There are no secondary nuclei. 



The Maturation Spindle. 



Later phases were studied exclusively in N. numismatis. The oocytes of 

 the March pupse no longer display the diminished staining capacity de- 

 scribed above. The diploid number of chromosomes is seen to be dispersed 

 throughout the nucleus, and the plasmosome is undergoing disintegration. 

 If, as is quite likely, there is a preliminary syndesis that synchronises with 

 the synaptic contraction in the young oocyte, this stage may be interpreted 

 as that of diakinesis. It is followed by an end-to-end pairing of the 

 chromosomes. In sections of the egg-mass taken from newly-hatched flies 

 at the beginning of April the chromosomes of the oocyte nucleus exhibited 



