48 



genus Cavolinia is placed at the end of a series of forms, provided with external calcareous 

 symmetrical shell, and is the most specialised genus in this direction. 



It seems quite superfluous to repeat all that has been already stated by the different authors, 

 especially van Beneden ^), Souleyet "), Gegenbaur ■'), Boas ^), and Pelseneer ^), who studied the 

 anatomy of the genus in question. I shall only restrict myself to a few remarks, partly not 

 agreeing with Pelseneer's publications, partly completing them. 



There are several differences between the two subgenera Dia er ia and Cavolinia (s. s/r.J. 

 Remarkable in Diacj'ia is the separation of the liver into two lobes, having each its own duet. 

 This arrangement does not occur in any other group of the Thecosomata. The flexure of the 

 intestine is ventral in all Cavoliniac-^ it seems unnecessary to state this again, had not Vogt 

 and YuNG ") been mistaken in this respect. 



It must have been a slip of the pen, which made Pelseneer pretend that the heart in 

 Cavolinia is on the ris^ht side. It is situated on the left. 



The genital gland in Diacria occupies the whole posterior portion of the visceral mass, 

 and is disposed transversely. In Cavolinia (s. str.J, ho wever it is asymmetrical, situated almost 

 quite on the left side, embracing the strong retractor muscle, while the lamellae of the gland 

 exhibit the usual direction as in all Cavoliniidae. Transverse sections through this organ show, 

 that the spermatozoids arise from inner folds of the membrane which envelops the gland. I 

 could not notice any regularity as to the disposition of the ova in the gland, as several ova 

 in different stages of ripening were found in the centre as well as at the periphery. According 

 to Gegenbaur (see above), the ova are produced in the outer parts of the lamellae, while 

 Knower ") States that "the youngest ova are found in the centre, immediately around the intra- 

 glandular portion of the duet, the oldest ova with considerable yolk at the periphery". I cannot 

 agree with either of these statements. Perhaps further histological investigations will throw 

 some light on the distribution of the ova in the genital gland. 



The efferent duet in Diacria arises from the dorsal surfaee of the gland, (|uite at the 

 right side, then runs over to the left, presenting the same eharacteristic elongated swelling as 

 in Clio and opens into the accessory genital glands. This swelling of the efferent duet was 

 also found in Cavolinia inflexa, contradictory to Pelseneer's statement, that this species "has 

 an ovoid vesicula seminalis, with a very short duet". 



In the other species of Cavolinia (s. sfr.J the efferent duet, proceeding from the right 

 concave side of the genital gland, is very thin, until a long vesicula seminalis, eoiled up at 

 the left side of the stomaeh, opens into it. This ve.sieula seminalis is sometimes provided with 

 small swellings from distance to distance ^). The accessory genital glands in Cavolinia fs. str.) 



1) Exerc. Zool., Mém. Acad. Sci. Brux., vol. XII, 1839. 



2) Voyage de la Bonite, vol. II, p. 100 — 136. 



3) Unters. über Pterop. u. Het. 1855, p. i — 40. 



4) Spolia atl. p. 86 — 91. 



5) Op. s. c. p. 17 — 21. 



6) Vergl. Anat. Bd. I, fig. 392 (p. 833). 



7) Pteropods with two separate sexual openiiigs, Ann. Mag. Nat. Hist. (6), vol. XIII, p. 529. 1S94. 

 8) Not ouly in Cavolinia loiigirostris^ as Pelskneer says, but also in Cavolinia tiidciilata. 



