144 George Lefevre 



embryos arising from these abnormal eggs possess the additional 

 chromatin, although I have found indications of such a condition, 

 but I shall attempt to investigate this point at a future time v^hen 

 adequate material may be at hand for the purpose. 



SUMMARY 



1 The unfertilized eggs of Thalassema mellita may be induced 

 to develop parthenogenetically into actively swimming trocho- 

 phores by immerison for a few minutes in dilute solutions of acids, 

 both inorganic and organic. 



2 After transfer from the acid solutions into normal sea-water, 

 the egg throws off a typical fertilization membrane, the germinal 

 vesicle breaks down, and maturation and cleavage follow. In 

 successful experiments, which were the rule, from 50 to 60 per cent 

 of the eggs developed into swimming larvae that could scarely be 

 distinguished from normal trochophores of a corresponding stage. 



3 The parthenogenetic development, in the majority of cases, 

 involves a strictly normal maturation, a normal cleavage, at least 

 in the early stages, and the usual processes of differentiation that 

 occur after fertilization by sperm. 



4 Gastrulation takes place in the normal manner, and the par- 

 thenogenetic larva possesses a digestive tract, differentiated into 

 mouth, oesophagus, stomach and intestine, and the prototroch 

 and apical plate bearing the normal arrangement of cilia. 



5 After maturation, the egg center disappears, and the cleavage 

 centrosomes arise de novo, probably without division of a single 

 primary center, and, when first seen, lie on opposite sides of the 

 egg nucleus which becomes the first cleavage nucleus. 



6 Cell division occurs mitotically throughout development, and 

 division of the nucleus is usually accompanied by cytoplasmic 

 cleavage. 



7 The number of chromosomes characteristic of the fertilized 

 egg is not restored, but the reduced number (12) is retained and 

 has been counted repeatedly, even in late stages. 



8 The rate of division is not as rapid, nor as regular as in normal 

 segmentation, and the parthenogenetic larvae, although swimming 



