400 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



The arguments in favor of parthenogenesis begin with that of 

 Perkins (1892), who believed that parthenogenesis must occur in the 

 parasites of Halictus tumulorum {Halictoxenos species) because out 

 of hundreds of parasitized bees he had never found a male parasite. 

 It is quite true that the males are seldom seen, for the writer is the 

 only one who has ever captured an Halictus with a male parasite. 

 This is no valid argument for parthenogenesis, however, because it 

 is quite possible that the presence of a male parasite renders the flight 

 of the host more difficult, or that observations were made at the wrong 

 time of the year. 



The next claim for parthenogenesis was set forward by Brues 

 (1903) in his studies of Xenos wheeleri Pierce in Polistes metricus 

 Say based upon his contention that — 



Two polar bodies are produced and the female pronucleus retreats toward the 

 center of the egg. It is closely followed by one of the polar bodies, presumably 

 the second ; the chromatin in its nucleus assumes the reticulate form, as does 

 also that of the second polar body, which has a much smaller nucleus and 

 protoplasmic body than the female pronucleus. When both have nearly reached 

 the center of the egg they place themselves side by side and finally fuse, giving 

 rise to the cleavage nucleus. 



And also because — 



There is no arrangement for the spermatozoa to reach the eggs without pass- 

 ing through the epithelium closing the internal ends of the oviducts and travers- 

 ing a considerable part of the fat body. 



Smith and Hamm (1914) consider Brues's evidence incomplete 

 because he did not follow polar body formation, but they advance 

 five reasons why they think parthenogenesis does occur. Their first 

 and second reason coincide with the second referred above to Brues : 



(1) There is no opening or apparatus in the female adapted for conveying 

 the spermatozoa to the eggs; (2) the eggs remain throughout their develop- 

 ment incased in the follicular epithelium of the ovary, so that access to them by 

 spermatozoa which had entered the body cavity is very difficult to imagine. 



The third reason is based upon Perkins's assertion concerning 

 Halictus. The fourth reason is that : 



The known stages in the polar body formation of Stylops are inconsistent with 

 tlie view that fertilization by a spermatozoon has been effected. 



Elsewhere they make a statement which does not agree with that of 

 Brues quoted above. 



In several females the eggs have been found in an early stage of development 

 the features of which strongly confirm our suspicion that development is parthe 

 nogenetic. In these cases all the developing eggs are at approximately the same 

 stage of development, exhibiting two or, in some cases, more segmentation 

 nuclei, while at the periphery of the egg a mitotic spindle is observed, which 

 invariably exhibits a single large chromosome and three or four smaller ones 

 often in process of division. Each egg is completely invested by the follicular 

 epithelium. 



