SKXIAL ORGANS. 39 



anil coiiipies.sL'il vvithiu the balance of the case. Upon coming 

 in contact with the water these spiral bodies commence moving 

 and finally burst throngh the thin end of the investing spermato- 

 phores dragging with them their sacks of spermatozoa. 



In Nantilns, \'an der lloevon has ascertaijied that the structnre 

 of the spermatophores is nuicli more simple. In this genus the 

 oviduct arises from a cliauiljer which communicates with that in 

 which the ovary is lodged. A large albumen gland 0[)ens into 

 the latter. 80 also the r«.s deferens, instead of originating 

 directly from the sack of the testes, communicates with it 

 through an intervening, chamber. 



The sexes in Sepia officinalis may be readily externally dis- 

 tinguished. There is in the first place a difference of coloration, 

 the females being unicolored, whdst the males have zebra-like 

 markings across the marginal tins and the dorsal arms — especially 

 when irritated. But the best means of distinction is in the 

 relative lengths of head with the arms, and body ; in the males 

 these two dimensions are about equal, but in the females the body 

 is only two-thirds the length of the head and arms. The cuttle- 

 bone in the female is much wider and more excavated behind. — 

 Bert, Mem. Linn. Soc. Hordeaux^x. 118. 



The most curious portion of the sexual histor}- of the cephal- 

 opoda is undoubtedly that which relates to their sexual union, 

 which is accomplished through the ofliices of one of the arms of 

 the male, which becomes modified in its structure for this pur- 

 pose. This arm, very unlike the others in appearance, sometimes 

 becomes detached from the animal during the sexual union, and 

 remains within the nuuitle of the female for a period, during 

 which it enjoys a separate life. Each genus seems t(^ be cliarac- 

 terized, not only by the particular arm, either on the right or 

 left side of the animal which is thus hectoootylized but also by 

 differences in its appearance and structure. The third left-side 

 arm of the Argonaut is first developed as a balloon-shaped sack, 

 which finally splits open and reunites its halves upon the dorsal 

 face of the arm which emerges from it, forming a chamber which 

 becomes filled with spermatophores, in a manner not yet under- 

 stood. Indeed the investigation of this whole subject may be 

 considered as yet in its infancy, and many points remain to be 

 cleared up : thus in some genera no sack for the reception of 



