MORPHOLOGY OF MELIBE 5G3 



Doridiiclae and Aeolidiidae, he found, were distinctly 

 male or female; among the Elysiidae all the follicles, in 

 fact, contained two genital products. Mazzarelli (1891 a) found 

 that, Avhile the hermaprodite gland is divided into lobes with 

 subdivisions somewhat deeply placed, each lobe presents a 

 great number of acini contrary to that wdiich up to that time 

 had been observed in tectibranchs — referring in particular 

 to the works of Lucaze-Duthier on Pleurobranchus, 

 of Moquin-Tandon on U m b r e 1 1 a , of Vayssiere on A p h a 1 a - 

 spidea, and by himself on the Aplysiidae — each acinus 

 produces at the same time and contains ova and spermatozoa. 

 In P 1 e u r o b r a n c h i a e a , however, there are both male 

 acini and female acini. 



Lang (1896) characterizes three types of genital ducts in the 

 molluscs as follows : 



Type I . — ' The hermophrodite gland has a single un- 

 divided efferent duct opening through a single aperture — 

 Gastropteron, Pteropoda, Cephalospedae(Bulla, 

 Dorium).' 



Type II, — 'The hermaphrodite gland gives rise to a 

 hermaphrodite duct which soon divides into two parts, the 

 vas deferens or -seminal duct, and the oviduct. The former 

 runs to the male copulatory apparatus, the latter to the female 

 genital aperture. The male aperture and the penis lie in front 

 of the female . . . both lie on the right. This second type may 

 be deduced from the first, if we assume that the common 

 duct of the hermaphrodite gland divided into a male and female 

 duct, but also that the seminal furrow closed to form a canal 

 in continuation of the male duct. To this type belong : 



1 . A few species of D e n d e b a r d i a 



2. B a s b m m a 1 p h r a , 



3. Oneida, and 



4. Vaginulidae 



of the Pulmonata 



Type III . — ' In all N u d i b r a n c h i a and a few T e c t i - 

 branchia (e.g. Pleurobranchiaea), the hermaphrodite 

 gland gives rise to a hermaphrodite duct, which, as in the 



p p 2 



