MOLLUSCA HETEROPODA. 423 



The Memoir by Krohu goes much further. (Anatomisch- 

 physiologische Beobachtimgen iiber die Sagitta bipunctata. 

 Mit eiuer lithograph. TafeL Hamburg.) The author, who 

 was unacquainted with Darwin's Memoir, divides the animal 

 into head, trunk, and tail. In the species described by 

 him there are only from five to seven unciform teeth, the 

 two internal minute denticles were also observed in this 

 instance. The head is separated from the body by a trans- 

 verse septum, and the body from the tail by a similar 

 septum. In the trunk there were likewise observable only 

 the intestinal canal and the two ovaries. The latter open 

 by two orifices on the back, between which on the abdomen 

 the anus is situated in the middle. Heart, vessels, 

 branchiae, and liver were not observed. The two cavities 

 in the tail are seminal receptacles, and the circulating 

 granules, which Darwin regarded as undeveloped ova, con- 

 stitute bundles of spermatozoa, which are thread-like, at- 

 tenuated at each extremity, and exhibit serpentine move- 

 ments. These seminal receptacles open on each side 

 anteriorly to the caudal fin, in a small papilla which is 

 hollow, and to which leads a small canal, becoming narrower 

 as it advances outwardly. These animals, consequently, 

 are androgynous, and the author believes that, in them, 

 self-impregnation takes place, because at a time when 

 spermatozoa are found in the ovaries the seminal recep- 

 tacles are always empty; this, however, appears to me 

 improbable, from the distance of the male genital orifice 

 from the female. Copulation, however, has not yet been 

 observed. The nervous system consists of an hexangular 

 cephalic ganglion, from which arise anteriorly two filaments, 

 which on the muscles of the unciform teeth are expanded 

 into a ganglion 011 each side ; posteriorly also two filaments 

 are given off, which, at the border of the cephalic portion, 

 are united in such a way as to constitute a loop. At their 

 origin also two delicate nerves arise, which proceed to the 

 two black eye-points situate on the upper surface of the 

 head. Lastly, two filaments arise laterally from the cephalic 



