period. But it is surprising that a mollusc with such re- 

 markable exteiTial cliaracters has not been the object of any 

 special rosearchf rom tlie foundation of comparative anatomy 

 up to the present time. It is necessary to come to the year 

 184G to find a naturalist who has taken for the subject of 

 his observations this mollusc so unfortunately celebrated. 



Since the appearance of the memoir of Quatrefages , 

 no detailed accoiont of the whole organization of Teredo has 

 appeared. Only in comparative treatises has it been taken 

 up. The principal of these are the papers by Grobben (4) on 

 the pericardial glands in Lamollibranchs , by Iv'enegaux (ll)on 

 the circulatory system in Lamellibranchs ; and by Pelseneer 

 (14) in :iis extensive comparative studies in the group. 

 Grobben first observed the anterior adductor muscle in Tore 

 do and proved the Teredinidae to be dimj'arians. Aside from 

 this point, the figure of Teredo thai he gives is v/holly un- 

 reliable. J.'enegaux attempted to establish the homologies of 

 the aortae, and Pelseneer described the visceral ganglion 

 and related structures. I shall have occasion to refer to 

 these papers in special i)arts later, and it v/ill be seen 

 that the comparative method of study is not alvirays satisfac- 

 tory, ii' the examination of special foi-ms be not made witli 



