ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 59 



The next set of changes, which occur in animals 7-9 mm. long, give the 

 generative organs their definite form ; the primary duct continues to divide 

 into two, and is continued distally into the penis, so that now the male and 

 female ducts arise directly from the cavity of the penis. The small out- 

 growth at the base of the penis, in which may be recognized the rudiment 

 of the vas deferens, increases in height, against the side of the female duct, 

 into which it opens when the walls at the point of junction become absorbed. 

 The flagellum appears as a blind diverticulum which arises at the base of 

 the penis ; at its blind end two secondary c^ecal vesicles early become 

 apparent. The prostate glands are developed as small outgrowths of the 

 female duct proximal to the connection with the vas deferens. The rudi- 

 ment of the receptaculum seminis was first seen in an animal about 12 mm. 

 long, where it appeared as a short wide-necked outgrowth of the penis ; it 

 arises just below the orifice of the atrium. 



We may note the following general considerations as results of this 

 investigation ; the portion of the duct which is temporarily separated off 

 alone appears to be the homologue of the male ducts of the most closely 

 allied forms in which there are separate efferent ducts ; the single genital 

 orifice is the homologue of the female orifice of the Basommatophora, while 

 the male orifice is only a secondary product of the penis; the seminal 

 groove and the prostate glands of the Stylommatophora are a product of the 

 female duct ; the anatomical relations of the ducts of the Stylommatophora 

 must not be derived from that of the Basommatophora by supposing that 

 there has been a secondary fusion of the two ducts. The generative appa- 

 ratus of the Basommatophora may be derived from that of the Stylomma- 

 tophora, but the converse proposition is not permissible. There can be no 

 doubt that the penis and vas deferens are neomorphs, developed within the 

 limits of the phylum of the Pulmonata. 



When we extend our survey to another group of Gastropod Molluscs, we 

 find we are justified in saying that the permanent disposition of the genera- 

 tive organs of the Prosobranchiata is temporary in the Pulmonata. The 

 latter are laid down and developed on the female type, and only become 

 hermaphrodite by the late appearance of modifications, which are, develop- 

 mentally, ucessential ; when purely female forms are seen we must not 

 explain the phenomenon by regarding it as atavistic, but simply as a more 

 forcible marking of the female type which is normally predominant in 

 development. The author reminds us that, in an earlier study, he showed 

 that the generative organs of the least constantly or inconstantly herma- 

 phrodite bony fishes are formed on the female type. The male genital duct 

 is not a permanent structure, but disappears towards the end of development 

 without leaving a sign of its presence. 



The author concludes with a few notes on the anatomy and development 

 of other systems of organs. The structural relations of the secreting cells 

 of the foot-gland are of interest, as there are in the adult three different 

 forms of cells. The epithelium of the basal portion forms two ciliated 

 ridges, and is sharply marked off from the pavement epithelium of the side 

 walls. At the base of the groove the sensory cells, as Sochaczewer called 

 them, are situated; Dr. Brock demurs, however, to this view of their 

 function, and thinks that they are nothing more than ordinary cells between 

 which the glandular cells open into the efferent duct, and which are 

 specially modified thereto. On the roof the cylindrical cells are low and 

 devoid of cilia ; they are specially remarkable for the longitudinal striation 

 of their protoplasm. The glandular cells are generally arranged in two 

 chief masses on either side of the efferent duct ; they are not so arranged 

 as to form compact masses, but only five or six cells form a connected 



