1 1 8 George Lefevre 



ot the larger blastomere in a plane parallel to the first, so that 

 three nearly equal cells were formed in a row, as shown in Fig. 14. 

 One of the commonest abnormalities, and one which might be 

 observed at any stage of the development, was due to the failure 

 of one or more cells to undergo cytoplasmic cleavage when the 

 nucleus divided, and, as a result of this condition, large multi- 

 nucleated cells might be found in embryos of all ages. Some 

 examples of such cases as these will be referred to below. 



Owing to departures from the normal type of cleavage, young 

 blastulae are occasionally produced in which the cleavage cavity 

 is not closed; this results in the formation of a cylindrical embryo 

 which is open at both ends. An optical sectit)n of this modified 

 blastula, showing the cells radially arranged around the cavity, 

 is drawn in Fig. 15. 



Although grastrulation usually takes place in parthenogenetic 

 development in quite a normal manner, disturbances in the pro- 

 cess do occur and produce a great variety of pathological embryos. 

 Many degrees of incompleteness in gastrulation may be seen, the 

 extreme case being one in which only a very few entoblastic cells 

 sink into the cleavage cavity- Such embryos, although they may 

 be ciliated and externally resemble trochophores, are found upon 

 sectioning to be merely large, hollow, spheroidal bodies in which 

 the enteron is represented by a few scattered ento meres. 



Amoeboid activities, which have been observed so commonly in 

 the parthenogenetic eggs of echinoderms and worms, are very 

 rare in the eggs of Thalassema, and when they occur at all, the 

 formation of pseudopodia is not extensive and takes place very 

 sluggishly indeed; Fig. 16 represents about as pronounced a case 

 as I have seen in my experiments. 



Fusion phenomena, which were so conspicuous in the experi- 

 ments of Loeb ('01) and especially in those of Lillie ('02), after 

 treatment of the unfertilized eggs of Chaetopterus with KCl and 

 CaClj solutions, were entirely absent in Thalassema. In Chaetop- 

 terus, eggs may fuse into masses which show certain differentiations 

 and form giant, ciliated structures and double, triple, quadruple, 

 etc., monsters. Lillie, for example, has described fusion masses, 

 into the composition of which about 100 eggs had entered, and 



