HABITS, ETC., OF CEKEBliATULUS LAOTEUS. 145 



side of the connecting isthmus. A large papilla was formed 

 on the same blastoniere to which the polar bodies were 

 attached^ and a moment later a similar one appeared on the 

 other blastomere (fig. 47). Short spin-threads radiated 

 from both papillae ; then the first papilla disappeared, but 

 the spin-threads remained and formed quite a stout thread 

 extending across the groove (fig. 48). In some eggs the 

 threads first formed remain until those upon the opposite 

 side of the isthmus have appeared. These eggs are of 

 special interest, because they show that the spin-threads 

 contain contractile protoplasm (fig. 51). The two blasto- 

 meres were drawn together on the side of the isthmus farthest 

 from the polar bodies, and held for an instant and then re- 

 leased. During this contraction the spin-threads shortened 

 and thickened visibly, showing that they were at least active 

 agents in the process. The papillas also were pulled out 

 slightly in the direction of the spin-threads, as would be 

 expected of yielding protoplasmic material. After an in- 

 terval of five seconds the blastomeres were pulled together 

 again, this time on the side nearest the polar bodies. These 

 movements on opposite sides of the isthmus alternated at 

 irregular intervals for two minutes, when the papillae had 

 entirely disappeared, and the blastomeres had been drawn 

 together and flattened. These contractile movements were 

 noted independently, and commented upon by a friend who 

 was watching another lot of eggs, and were observed several 

 times subsequently while studying other phenomena, so there 

 can be no doubt of their reality. It must be remembered in 

 judging these facts that the conditions are specially favour- 

 able in the present instance for the occurrence of just such 

 phenomena. Intercellular connections by means of spin- 

 threads have been clearly demonstrated in the eggs of many 

 Metazoa (cf. 3), and have even been retained in preserved 

 specimens. 



We should expect to find them in Cerebratulus as a natural 

 sequence to the marked spinning activities of the polar bodies. 

 The perceptible motion of the blastomeres is rendered possible 



VOL. 43, PART 1. NEW SERIES. K 



