78 



ON CLASSIFICATION, 



as a Nemertid — provided with the characteristic proboscis, and 

 the other organs of that group of Turbellaria. 



Fig. 37. 



Fig. 37. — Pilidium gyrans (after Leuckart and Pagenstecher). 



A. Young Pilidium ; a, alimentary canal ; b, rudiment of the Nemertid. 



B. Pilidium with a more advanced Nemertid. 



C. Newly-freed Nemertid. 



Many Trematoda, and all Tsenioid Scolecicla, again, present 

 an essentially similar process of internal gemmation, in virtue of 

 which either a separate offspring arises, or an adult is developed 

 within an embryonic form ; but in these cases the appropria- 

 tion of the intestine of the primary by that of the secondary 

 form, which renders the ordinary development of the Echinoderm 

 so striking, does not occur. 



In discussing the characters of the Echinodermata, I have 



