62 CLASSIFICATION. 



with the Pellibranchs, above all in the generative organs ; 

 this caused him to make a comparative revision of the geni- 

 tal organs of mollusks. He then ascertained that those be- 

 longing to his first division were androgynous and furnished 

 with a retractile male organ ; whilst those of the second section 

 were dioecious, with a non-retractile male organ ; and those of 

 the third section differed from the others by the want of a copu- 

 lative organ. In other words, he had thus arrived, inde- 

 pendently, at the three groups proposed in accordance with the 

 sexual organs by Blainville and Labreille. 



In 1859 Morch perceived that Mollusks were divided into two 

 great groups, according to the construction of the heart and that 

 these groups accorded also with those furnished by the sexual 

 organs. Thus the Phanerogama Latr. with a retractile or non- 

 retractile copulative organ, have a heart with a single auricle 

 (Monotocardia Morch), whilst the Agama Latr, which have no 

 copulative organ, have a heart with two auricles (Diotocardia 

 Morch). It appears, doubtless, rather strange that the acephala 

 should form a group with a considerable portion of the gastero- 

 pods (Rhipidoglossa and Heteroglossa), but there exists a simi- 

 lar division among the vertebrates, namely : the cold-blooded 

 vertebrates, where the fishes are united with reptiles, the latter 

 provided with well-developed locomotive organs analogous to 

 those of the mammalia. 



Stimpson proposed, a few years since,* to form a group Anan- 

 dria, characterized by the want of a male copulative organ. This 

 group includes the Melanians of North America, the Vermetidae 

 and Turritellidae and certain Ceritlmt. M. BAippel, however, 

 has figured a male organ in Yermetus inopertus, and M. Lacaze- 

 Duthiers has found a single male individual which circumstances 

 did not permit him to examine sufficiently. As to the Melanians, 

 they may want an external conical male organ, but the sexual 

 character is with them represented by a groove. In the Agama 

 of Latreille there is not the least external sexual difference. 



Mr. Morch believes that naturalists of the most opposite 

 schools could agree to a scheme of classification which he sub- 

 mits, as follows : 



* Am. Jour. Sci., 2 ser. 37, p. 47, 1864. 



