PRELIMINARY REPORT ON THE EARLY HISTORY 

 OF THE EGG AND EMBRYO OF CERTAIN 



HYDROIDS. 



CORA JIPSON BECKWITH. 



Within the last few years some of the hydroids (Pennaria, 

 Clava leptostyla, Endendrium, Tubularia crocca) have been de- 

 scribed as differing widely in their processes of maturation, 

 fertilization, and early cleavage from what we have come to 

 think of as typical. Other members of the same group (Tubu- 

 laria mesembryantheum, Clava squamata, H\dra, Gonothyrea, 

 JEquorea, Tiara, Gonioneinits} have been described as perfectly 

 typical. That certain of the hydroids should conform to the 

 type and others not, seemed improbable. The fact of the low 

 organization of the group which is used by Hargitt to account 

 for such variation seemed hardly sufficient. On this account at 

 the suggestion of Professors Morgan and Wilson, I undertook 

 the reexamination of two of the forms, Pennaria and Clava 

 leptostyla, which varied most from the type, to discover if pos- 

 sible the relation between the aberrations described in these forms 

 and the usual type. The results on Pennaria were worked out in 

 the winter of 1907 at the Zoological Laboratory of Columbia 

 University, on material collected at Woods Hole during the 

 previous summer. Those on Clava were obtained in the summer 

 and autumn of 1908. 



A brief review of Hargitt's work on Pennaria and Clava lepto- 

 styla will be necessary to recall the points which I wished to clear 

 up. In both these forms, according to his results, the processes 

 of maturation and fertilization of the egg are very obscure and 

 incapable of demonstration. The germinal vesicle just, before the 

 time that maturation should take place moves to the periphery 

 of the egg where it loses its staining capacity, the nuclear mem- 

 brane breaks down, and the nuclear substance becomes diffused 

 throughout the egg, where it is no longer recognizable, due 

 probably to some chemical or physical change in the egg. The 



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