HABITS, ETC., OF OEREBRATULUS LACTEUS. 99 



Introductoey. 



The ontogeny of the Nemerteans, and more particularly 

 that of the Schizo-nemerteans, is of special interest on 

 account of the metamorphoses through which the young 

 embryos pass. 



Ever since its discovery and naming by Miiller in 1847 

 (38) the pilidium form of larva has attracted the attention of 

 leading scientists the world over. As a result of their inves- 

 tigations we are to-day in possession of the leading facts 

 with reference to the histology of the pilidium and the meta- 

 morphoses from this free-swimming form into that of the 

 adult worm. 



Much work has also been done upon the origin and matura- 

 tion of the sexual products in different species. But our 

 knowledge of fertilisation, segmentation, and the early 

 history of the pilidium has been derived almost wholly from 

 two papers by Metschnikoff, one in 1870 (35) and another in 

 1882(36).^ 



The former paper I have been unable to examine, but from 

 the excellent abstract given by Burger (13) I judge that 

 Metschnikoff obtained the eggs already fertilised, and fol- 

 lowed their subsequent development as closely as possible. 



At all events he confines his attention in both papers 

 almost exclusively to the later development of the larva, and 

 seems to have derived his facts from observation of histolo- 

 gical material, and not from a study of the living embryo. 



' Since the above was written it has been my pleasure to receive from the 

 author, Dr. W. R. Coe, of tlie Sheffield Biological Laboratory of Yale 

 University, a copy of his excellent paper upon " The Maturation and Fertili- 

 sation of the Egg of Cerebratulus " (16). This is the first step toward 

 supplementing our knowledge of this long neglected group and is most 

 praiseworthy. 



