36 OPISTHOBRANCHIATA OF BRAZIL 



becomes modified in the course of the duct. At the proximal 

 end the spiral portion of the genital duct is continued into the 

 right half, while that on the left is prolonged into the duct of the 

 spermatocyst and the duct of Cuvier, the latter communicating 

 with the fertilization chamber. These relations may be more 

 readily made out in an immature than in an adult specimen, and 

 best of all, in serial sections. The spermatocyst is a pear shaped 

 sack, doubled upon itself, situated at the anterior margin of the 

 base of the adnexed genital mass, from which it projects freely 

 for the greater portion of its length. It is ca.' 4.9 mm. long 

 and 2.3 mm. in maximum diameter in the largest specimen 

 examined, but much smaller in the others. 



The large hermaphroditic duct extends from the adnexed 

 genital mass to the vulvar opening, with a length of 17.9 mm. and 

 a diameter of 0.5 mm. in the largest individual. It is externally 

 marked to correspond to its internal differentiation into two 

 ducts, the one on the right the ovo-spermatic, that on the left 

 the copulatory duct. The latter duct, beyond the entrance of the 

 duct of the spermatocyst, becomes the vagina. The outer surface 

 of the right of these ducts is of a yellowish brown color and 

 transversely rugose. The surface of the left half is smooth and 

 dark brown. At a distance from the vulvar opening of about 

 one-fifth the whole length of the large hermaphroditic duct, the 

 duct of the spermatotheca, or vesicle of Swammerdam opens into 

 the left or copulatory duct. The vesicle itself is a large, spherical 

 structure, 5.0 mm. in maximum diameter, lying immediately to 

 the left of the parieto-visceral ganglion. By a slender duct, 

 0.9 mm. in diameter and 6.2 mm. in length, in the largest speci- 

 men, it communicates with the copulatory duct. 



The right half of the large hermaphroditic duct, which 

 functions alike as oviduct and vas deferens, the ovo-spermatic 

 duct, the "ovidutto-deferente" of Mazzarelli, is continued forward 

 as a narrow external groove along the right side of the animal 

 from the genital opening to the right side of the head, close 

 below the right anterior tentacle. In the largest specimen the 

 external spermatic groove measured 85.00 mm. in length. Here 

 it is continued inward along the inner wall of the penis sheath 

 to its base, whence it recurves along the side of the penis to its 

 tip, thus forming a conduit for the spermatozoa in copulation. 



