49 



are situated either on the left side of the stomach or ventrally to it-, the albuminiparous gland 

 is situated at the right anterior corner of the muciparous gland. 



In Diacria there is a pyriform receptaculum seminis, while in Cavolinia (s. str.) the 

 receptaculum seminis is scarcely visible, situated on the ventral side of the muciparous gland '), 

 and with a very short duct. 



Knower has described in Cavolinia lotigirostris a second sexual opening, leading from 

 the muciparous gland directly into the mantle-cavity. He says: "on the left side of the uterine 

 gland, sections in all planes show a second opening from the reproductive system to the 

 exterior. This is a slit-like aperture on a slight papilla, on the anterior surface of the visceral 

 sac and to the left. The opening leads directly into a ciliated fold of the uterine gland, the 

 ciliated cells of which turn out at the lips of the aperture and become continuous with the 

 epithelium of the external surface of the body". 



I have also found this opening in Cavolinia longirostris, after examining series of 

 transverse sections. In Cavolinia tridentata I could not see it. In the first species the opening 

 just described was not on the left side of the muciparous gland, but on the dorsal surface. 

 The cavity of the muciparous gland, developed at the right side, communicates with the mantle- 

 cavity by an exceedingly small aperture, bordered by lips which exhibit the same histological 

 structure as the external epithelium of the muciparous gland. This aperture is perhaps a vaginal 

 opening, as Knower thinks; I must confess that the explanation of this second opening, never 

 found in any other Thecosomatous "Pteropod", is not clear to me at all. Among the Bulloidea 

 Lobiger and Actacon also have a separate opening for each sex. 



The ciliated seminal groove, leading to the penis, has become a closed ciliated tube in 

 Cavolinia longirostris, as Knower already discovered. 



As to the central nervous system, the form and disposition of the different ganglia is 

 the same as that, found in all Cavoliniidae. I cannot, however, agree with Pelseneer that 

 the pedal ganglia in all the species of Cavolinia show an anterior pedal commissure. This 

 commissure does exist, according to my own investigations, in the subgenus Diacria and in 

 Cavolinia inflexa, but I could never succeed in finding it, neither after most careful dissection 

 nor in a series of transverse sections, in the other species of Cavolinia (s. str.). In these species 

 each pedal ganglion has a very large ganglionic cell on its proximal median side, but a second 

 pedal commissure does not exist here. The visceral mass is asymmetrical; the pallial nerves, 

 issuing from it, are very strong. From the anterior side of each cerebral ganglion (at least 

 in Cavolinia tridentata., particularly examined on this point) rises only one tentacular nerve 

 which, however, divides into several branches (PI. II, figs. 78, 79). 



The buccal ganglia are fused together into a single triangular mass, attached to the cerebral 

 ganglia by a commissure. The nerves issuing from the buccal mass are disposed in the same manner 

 as in Clio. This conformation of the buccal ganglia is characteristic for all the Cavoliniidae. 



l) To my opinion, Knower (see above) has mistal<en the distal end of tlie efferent duct iu Cavolinia lo/tgirostris for a 

 seminal receptacle. 



SIBOGA-EXPEDITIE LII. 



