Manchester Memoirs, Vol. Ixii. (191 7), No. 2 



II. Natural and Artificial Parthenogenesis in Animals. 



By D. Ward Cutler, M.A. (Cantab) 



Assistant Lecturer and Demonstrator in Zoology in the Victoria University 

 of Manchester. 



Parthenogenesis, the production of an organism from an egg 

 which has not been previously fertilised by the male element or 

 caused to develop by artificial means, is of common occurrence 

 in the animal kingdom, though, ass wjill be seen, confined to but 

 few of its great divisions. 



This phenomenon has been long known, but until recently /was 

 not regarded as of much importance in relation to general 

 biological problems. The cytological discoveries and the work 

 that has been done on the probjean of the cause 1 of sex has, how- 

 ever, brought into prominence the importance of parthenogenesis. 



In 1906, a paper on the cytological aspect of parthenogenesis 

 in Insects was published by Hewitt in the Memoirs', of this Society, in 

 which he reviewed the principal work that had been done up to that time. 

 Since then the number of publications have increased enormously, 

 and some of the conclusions recorded in Hewitt's paper have 

 proved to be erroneous. I feel, therefore, that it may be of use 

 to bring together some of the most important results which have 

 been obtained by recent workers, and to indicate their bearing 

 upon a few general biological problems. Passing in review the 

 principal divisions of the animal kingdom in which partheno- 

 genesis is known to occur, it is found that the Arthropoda afford 

 by far the most numerous examples. Among the Crustacea, most 

 of the Cladocera and very many of the Ostracoda are capable of 

 producing parthenogenetic eggs, and in almost all the groups of 

 Insects some examples can be found. Outside the Arthropoda 

 many of the Nematoda habitually reproduce by this method and 

 in other invertebrate groups a few cases can be cited. 



In Order, however, to obtain a clear understanding of much 

 that follows in the paper it is necessary to realise that the sex of 

 the animal produced by parthenogenesis is not always the same, 

 and that the interpolation of this method of reproduction causes 

 complicated life cycles to occur. 



