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The Maturation and Fertilization of the Egg 

 of Cerebratulus. 



By 

 "Wesley R. Coe, New Haven, Connecticut. 



With Plates 19—21. 



While enjoying the privileges of the Zoological Station at Naples ^) 

 during the spring of 1896, I obtained several series of preparations 

 of the eggs of Cerebratulus marginaius Eenier. This is one of the 

 largest species of Nemerteans found at Naples, and one which may 

 always be obtained in abundance. Some of these preparations were 

 so beautiful and showed the details of structure so clearly, that they 

 gave promise of throwing additional light on some of the intricate 

 problems connected with the maturation and fertilization of the egg. 

 They seemed the more worthy of careful study because of the fact 

 that no detailed account of the phenomena taking place within the 

 egg previous to its cleavage had been given for any member of this 

 group of worms. 



As was to be expected, the general course of development of the 

 egg up to the time of cleavage is found to agree closely with that 

 of other animals; yet in certain details these eggs present features 

 which are different from those described for any others. 



unfortunately, the eggs of C. marginaius are so opaque that it 

 is impossible to follow the internal changes in the living egg, and 



1) The writer is under obligations to Dr. Alexander Agassiz and 

 to Prof. Anton Dohrn for the privileges afforded him at the Zoological 

 Station at Naples, as well as to Prof. C. 0. Whitman for the hospitality 

 of the Marine Biological Laboratory at Woods Holl, Mass. It is 

 likewise a pleasant duty to acknowledge the many valuable suggestions 

 received from Prof. S. J. Smith. 



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