102 • CHAS. B. WILSON. 



The Adult Worm. 

 Determination of Species. 



The species under consideration is one of the largest of 

 the Nemerteans, and possesses all the characteristics of the 

 group. These consist negatively in the absence of all external 

 appendages and of a definite body-cavity, and the entire lack 

 of visible segmentation. Positively they include the posses- 

 sion of a smooth body, flattened dorso-ventrally, and of a 

 very long tubular proboscis, which can be protruded by 

 eversion from an aperture in the front of the head. 



Much work has been done upon the classification of the 

 Nemerteans with no decisive results. Different species and 

 even genera frequently resemble one another so closely that 

 they cannot be distinguished after preservation. Hence we 

 can find in the attitude of different authors every variation 

 from one (46) 75 per cent, of whose enumerated species are 

 new creations, to another (27) who would include all the 

 Schizo-nemerteans under a single genus. And our present 

 species is classified by different authors under distinct names 

 and even under different genera. The name we have chosen 

 is the one selected by Verrill, but the same species was called 

 by Girard Meckelia f ragilis, by Leidy Meckelia ingens, 

 though at first he designated it M. lactea. The name of 

 the group, Nemerteans, was first applied by Cuvier, and is 

 derived from Nemertes, one of the Mediterranean sea-nymphs, 

 daughters of Nereus and Doris. 



The generic name, Cerebratulus, was first given by 

 Eenier in 1804 to a single species, and continued until re- 

 cently to be simply a specific name. It is derived from 

 cerebrum, the brain, probably from a fancied resemblance 

 of the tissues (41). 



The specific name, lac tens, was given by Leidy to cer- 

 tain small white specimens, which afterwards proved to be 

 the young of this species, and accordingly the name was 



