318 INTRODUCTION TO CYTOLOGY 



feeble trophic powers, rendering it quite unfitted for independent repro- 

 duction, rather than from any inherent difference between the two 

 sexes in relation to reproductive activity." 



Many normally parthenogenetic animal eggs are known to have the 

 diploid chromosome number as the result of a failure of reduction, a 

 condition paralleling that known as ooapogamy in plants. On the 

 contrary, there are some which, unlike any known vascular plant, are 

 haploid, reduction having taken place in the normal fashion. Partheno- 

 genesis is often associated with certain irregularities in the behavior 

 of the polar bodies, as will be noted in the following descriptions of some 

 well known examples. In the majority of recorded cases the partheno- 

 genetic egg produces but one polar body; in some, however, two are 

 formed as in all zygogenetic eggs (those developing after having been 

 fertilized). 



It was long ago noticed by Blochmann (1888; see Wilson 1900, pp. 

 281-4) that in Aphis both zygogenetic and parthenogenetic eggs are 

 produced; the former produce the usual two polar bodies while the 

 latter have but one. It was also seen that the polar bodies are not 

 budded off as separate cells, but remain within the membrane of the 

 egg. Weismann (1886, 1887), working on rotifers, concluded that the 

 second polar body has something to do with parthenogenetic develop- 

 ment; and Boveri (1887d, 1890), who had seen the chromosomes of the 

 second polar body transform themselves into a nucleus in the egg of 

 A scam, made the suggestion that this second polar body might unite 

 with the egg nucleus and so initiate development. Brauer (1894) an- 

 nounced that this is precisely what occurs in Artemia, a phyllopod 

 crustacean. In this organism two types of parthenogenesis are found. 

 In some cases the nucleus of the second polar body, with 84 chromosomes, 

 actually does unite with the egg nucleus, likewise with 84, causing 

 "fertilization" and the resulting development of an individual with the 

 diploid number (168) of chromosomes. In other cases only one polar 

 body is produced, but reduction is accomplished in the division forming 

 it, and the resulting haploid egg develops parthenogenetically into an 

 individual with only 84 chromosomes. 



In Phylloxera carycecaulis (Morgan 1906, 1908, 1909, 1910, 1915) 

 only one polar body appears, but here no reduction occurs: the diploid 

 egg develops parthenogenetically. In Nematus lacteus (Doncaster 1906) 

 two polar bodies are produced, but reduction fails and the diploid egg 

 proceeds to develop as in Phylloxera. 



It has long been known that the eggs of the honey bee, Apis mellifica, 

 will develop either zygogenetically into females or parthenogenetically 

 into males. It has been shown in both cases that there are two polar 

 bodies (Blochmann) and that a normal reduction in the number of 

 chromosomes occurs (Nachtsheim 1912, 1913). The fertilized eggs 



