134 PARTHENOGENESIS [CH. 



the spermatocyte divisions is suppressed. This was first 

 discovered by MEVES (1907) in the Hive Bee; it has since 

 been observed in other bees, and in Wasps, Sawflies and 

 Gall-flies. In most species the spermatocytes undergo only 

 one division, in which the chromosomes divide equationally, 

 so that the spermatids contain the same number of chromo- 

 somes as the spermatogonia. Traces of a first division may 

 occur in the formation of a spindle in which the chromo- 

 somes do not divide, followed by the separation of a minute 

 piece of cytoplasm containing one of the centrosomes 

 (PI. XIV). In the Hive Bee a curious and at present un- 

 explained modification of this process is found (PL XV). 

 After a first abortive division, in which a small piece of 

 cytoplasm is separated from the spermatocyte, a fresh 

 spindle is formed; one pole of this spindle extends into a 

 long finger-like projection of the cell, at the apex of which 

 is the centrosome. The chromosomes divide, and one group 

 passes into the projection and forms a vesicular nucleus, 

 while the other group forms a nucleus in the body of the 

 cell. An extremely unequal cell division then occurs, by 

 which the nucleus in the narrow projection is separated 

 almost without any accompanying cytoplasm from the rest 

 of the cell. The cell, now a spermatid, proceeds to develop 

 in the normal way into a spermatozoon, while the extruded 

 nucleus, after passing through similar stages for a time, 

 gradually degenerates. No adequate explanation of this 

 "polar-body formation" by the spermatocytes of the Hive 

 Bee has yet been given, and in other Hymenoptera, in- 

 cluding the Humble Bee, the spermatocytes divide equally 

 (cf. PI. XIV). 



In all the species mentioned hitherto under this heading 

 the eggs which develop parthenogenetically give rise to 

 males; this is sometimes called arrhenotokous partheno- 



