Germ Cells of Leptinotarsa Signaticollis. 187 



A knowledge of whether this bi-partite nucleolus represents 

 one or two chromosomes may be of no great importance in itself, 

 but it has a very important bearing in determining the relation of 

 the nucleolus to the segments of the spireme in synapsis. The 

 manner in which synapsis takes place in insects is scarcely at all 

 understood. The critical stages are just the ones that are omitted 

 in descriptions or passed over so hurriedly that the reader is 

 usually left to follow his own choice in the matter. 



Wilson ('09 a) in a admirable series of photographs, has produced 

 evidence against the idea supported by Montgomery ('00), 

 Sutton ('02), Stevens ('03) and Dublin ('05) and others, that 

 synapsis occurs in the closing anaphases of the last spermatogonial 

 division. He has shown that inPyrrochoris the number of chromo- 

 somes in the postphases following the last spermatogonial 

 division is not the reduced number, but approximately the 

 somatic number. Synizesis does not follow immediately but is 

 separated by a long resting period. 



The extreme synizesis stage in the male of signaticollis is shown 

 in Fig. 45, where the chromatin is in the form of a tightly wrapped 

 split spireme. The double nature of the spireme is seen to better 

 advantage in Fig. 46, where it is unfolding. As the number of 

 its segments is greater than the reduced number of chromosomes, 

 synapsis in the sense of an actual fusion has not yet taken place. 



In the ovocyte, following the last ovogonial division, prac- 

 tically the same condition occurs. It happens that in the particu- 

 lar instance shown in Fig. 39 the two halves of the spireme are 

 separated; which indicates very clearly the double form of this 

 structure. Similar examples are not wanting in the spermatocyte. 

 As one studies the succeeding stages shown in Figs. 41, 42 and 

 43, it is clear that no reduction has yet occurred. 



Actual conjugation of chromosomes does not take place in the 

 last stages of the spermatogonial or ovogonial divisions, although 

 the chromosomes at this time do seem to pair into two homologous 

 series which in synapsis have the appearance of a split spireme. 



It is rather questionable whether synizesis indicates an actual 

 contraction of the chromatin; at least in the material under 

 consideration. In Fig. 46 it seems to mark the unfolding or dis- 



