ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 205 



Lefevre has made a very interesting observation on the 

 behavior of the polar bodies. As a rule, the first polar body 

 given off from the egg when it is fertilized with sperm divides 

 only once, and the second polar body does not divide. Lefevre 

 observed, however, that both polar bodies of the eggs treated 

 with acid pass through a series of mitotic divisions and give 

 rise to miniature embryos of sixteen cells. He compares these 

 facts with Francotte's observation that in Prostheceracus, a 

 turbellarian, the first polar body is relatively large and can be 

 fertilized by a spermatozoon and even develop into a gastrula. 

 As a rule the cleavage was normal and so were the larvae; 

 but they did not rise to the surface of the water like those 

 derived from fertilized eggs. Hence they easily fall victims to 

 bacteria. 



6. For the sake of completeness, some of the older experi- 

 ments on artificial parthenogenesis in annelids may be briefly 

 mentioned, although the methods used are not very satisfactory. 

 In Amphitrite eggs could be caused to develop by treating them 

 with sea-water whose calcium content was raised. 1 



Fischer produced artificial parthenogenesis in the eggs of 

 Nereis by treating them with a hypertonic solution. 2 Bullot 

 succeeded by the same method, in the eggs of Ophelia. 3 



Again we may state that the methods of artificial partheno- 

 genesis for annelids are essentially identical with those used for 

 the eggs of the sea-urchins, except that the second factor is 

 not quite so important. 



1 Loeb, Fischer, and Neilson, Pfliiger's Archiv, LXXXVII, 1, 1901; Scott, 

 Jour. Exper. ZooL, III, 49, 1906. 



2 Fischer, Am. Jour. PhysioL, IX, 100, 1903. 



3 Bullot, Archiv f. Entwicklungsmechanik, XVIII, 161, 1904. 



