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A. J. GOLDFARB. 



nated, and these were in nearly every instance, clusters of two. 

 The separation of the embryos of Arbacia occurred in exactly 

 the same manner as described by Driesch. 



These permanently agglutinated plutei may be attached to 

 one another at any angle as in Figs. 85, 86 and 87. In Fig. 85 

 the plutei are attached by their oral ends; in Fig. 86, the oral end 

 of one is attached to the side of the other, and in Fig. 87 a group 



of five plutei are agglutinated at various angles. As in the 

 previous stages of development one finds here also, that the 

 agglutinated partners may develop at different rates, the one 

 a pluteus, the other a blastula as Fig. 88, or a pluteus and a 

 gastrula, Fig. 89. 



Driesch described the following types of plutei from his 

 cultures : 



(a) True twins, i. e., agglutinated plutei. 



(&) Twins with a common blastoccele, i. e., body wall partially 

 fused, internal organs double. 



(c) Twins with a reciprocal influence on growth, a true fusion 

 with an enlargement of the body. 



