Artificial Parthenogenesis in Thalassema Mellita 97 



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 mally differentiated organs. That a far more normal result, how- 

 ever, has been obtained in the parthenogenetic development of 

 Thalassema will be pointed out in the following pages. 



Ill MATERIAL AND METHODS 



Thalassema mellita inhabits the dead tests of the sand-dollar 

 Mellita pentapora (Gmelin) and occurs abundantly on the exten- 

 sive shoals in the harbor of Beaufort, N. C. The egg is a parti- 

 cularly favorable one for experimental work in artificial partheno- 

 genesis. With a little experience one has no difficulty in distin- 

 guishing the sexes by the difference in color of the sexual products 

 which show through the semi-transparent body wall, the sperma- 

 tozoa appearing a milky-white and the eggs a light golden-yellow. 

 Males and females may, therefore, be separated, and it is not 

 necessary to touch the former during the course of an experiment. 

 The full-grown oocytes are contained in the segmental tubes which 

 fill a large part of the body cavity, and upon rupture of the tubes 

 great numbers of eggs may be obtained in perfectly clean cultures, 

 entirely free from immature eggs, slime and debris of all kinds. 



Every precaution was taken to avoid contamination by sperma- 

 tozoa, and it may be stated at the outset that in all experiments 

 the control eggs were absolutely negative and never showed a single 

 case of cleavage or differentiation of any nature whatever. 



The female worms were first separated from the males and kept 

 by themselves in a dish of sea-water over night. Before using, 

 they were thoroughly washed in fresh water, as were the dishes 

 and instruments employed in the experiment and the hands of 

 the operator. The body wall was then slit open, whereupon the 

 tubes, gorged with eggs, burst out through the opening. The 

 tubes were first rinsed in sterilized sea-water, in order to remove 

 the blood adhering to their surface, and then snipped off and 

 dropped into a dish of sea-water which had previously been raised 

 to a temperature of 70° or 80°. 



The eggs, when first removed from the tubes, are collapsed and 

 pressed out of shape, as a result of close packing in the confined 

 space, and do not become spherical until after fertilization by the 



