454 THE ANATOMY OF INVERTEBRATED ANIMALS. 



symmetrically - disposed oviducts, in the females of some 

 species ; but in most female, and almost all male, Cephalo- 

 pods 1 it has only one duct, the termination of which is usually 

 situated on the left side, but may be near the middle line 

 (male Nautilus), or even on the right side (female Nautilus). 

 In the female, the oviduct, or oviducts, present glandular en- 

 largements. In addition, two lamellar nidamental glands are 

 developed upon the walls of the branchial cavity, and to these 

 accessory glands may be added. These glands secrete a vis- 

 cid fluid, which invests the ova, and connects them, when laid, 

 into variously-shaped aggregations. In the male, a prostatic 

 gland furnishes the material of the cases, or spermatophores, 

 in which packets of spermatozoa are contained, and which 

 sometimes possess a very complicated structure. 



In the Dibranchiata, the spermatophores are slender 

 cylindrical bodies which may reach half an inch in length. 

 They have an external structureless case, thinner at one end 

 than the other, and often ending in a fine filament at the thin 

 end. Within this case, filling its thicker end, and as much as 

 half or two-thirds of the rest of its cavity, is a delicate sac 

 full of spermatozoa. 



The rest of the case is occupied by a very singular elastic 

 body, in form somewhat resembling the sponge of a gun with 

 a spiral screw turned on the handle. The enlarged "sponge" 

 end of this body is fastened by a delicate prolongation to the 

 spermatic sac, while the " handle," being too long to lie 

 straight, is coiled up at the end opposite to the sponge, and 

 then fastened to the outer case. When these bodies come 

 into contact with water they undergo strange contortions, 

 and finally, the thin end of the case giving way, the spring 

 frees itself, starts out of the case, and drags with it the sper- 

 matic sac. 2 



In JVautilus, according to Van der Hoeven, the spermato- 

 phores have a much simpler structure. 



The male Cephalopods are distinguished from the females 

 by the asymmetry of their arms, one or more of which, on 

 one side, are peculiarly modified, or hectocotylized. 



Some Cephalopods are devoid of any shell, but most pos- 

 sess a pallial shell, which is either external or internal. In 

 the former case, the visceral sac is lodged within that part of 



1 Keferstein found two ducts in a male Eledone moscTiata. 



2 For the minute structure of these curious spermatic cartridges, see Milne- 

 Edwards's elaborate essav, "Observations sur les Spermatophores des Mol- 

 lusques Cephalopode3." (" Annales des Sciences Naturelles," 1840.) 



