25t) CLASSIFICATION. 



and Terebra \ In 1 85t , Mfirch reduced the five principal divisions 

 to three, namely : 



I. Musivoglossata (corresponding to the Ptenoglossataof 1856, 

 but thus modified because this name has been used by M. Troschel 

 to characterize the group of Janthinsse and Scalariaa), Pulmonata 

 and Tectibranchia. 



II. Arthioglossata, including: 1. Taenioglossata ; 2. Ancis- 

 trogiossata ; 3. Toxoglossata. 



III. Rhipidogiossata, with the section Orthodonta (Cyclo- 

 branchiates). 



In 1861-2, circumstances having induced Prof. Morch to study 

 the Planarians, he v^as struck with their great affinity with the 

 Pellibranehs, above all in the generative organs ; this caused 

 him to make a comparatiA^e revision of the genital organs of 

 mollusks. He then ascertained that those belonging 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 diflered 

 from the others by the want of a copulative organ. In other 

 words, he had thus arrived, independently, at the three groups 

 proposed in accordance with the sexual organs by Blainville 

 and Latreilie. 



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, Miirch). It appears, doubtless, rather strange that 

 the acephala should form a group with a considerable portion of 

 the gastropods (Rhipidoglossa and Heteroglossa), but there 

 exists a similar division among the vertebrates, namely : the 

 cold-blooded vertebrates, where the fishes are united with rep- 

 tiles, the latter provided with well-developed locomotive organs 

 analogous to those of the mammalia, 



Stimpson proposed (Am. Jour. Sci., 2 ser. 8t, p. 47, 1864), to 

 form a group Anandria, characterized by the want of a male 

 copulative organ. This group includes the Melanians of North 

 America, the Yermetidae and Turritellida3 and certain Cerithire. 

 M. Eiippel, however, has figured a male organ in VermetuAi 

 inopertas., and M. Lacaze-Duthiers has found a single male 

 individual which circumstances did not permit him to exanaine 

 sufficiently. As to the Melanians, they may want an external 

 conical male organ, but the sexual character is with them repre- 

 sented by a groove. In the Agama of Latreilie thei'e is not the 

 least external sexual difference. 



