CEPHALOPODA. 



211 



structure, therefore, is a decided approach to the Vertebrate type of 

 organisixtiou. 



The sexes in all the Cephalopoda are in different individuals, and 

 the reproductive process in the Cuttle-fishes is attended with some 

 singular ])henoniena. The most remaikalile point in this connection 

 is the modification of one of the arms of the male Cuttle-fishes, for 

 the purpose of conveying the male element to the female. The 

 details of the modification vary in different spiecies of.Cuttle-fisli. 



In some of the Cuttle-fishes the modified arm becomes the recep- 

 tacle of the spermatozoa, but is not itself actually detached fiom the 

 animal. In some cases, however', as in the Pa])er Nautilus {Arcjo- 

 nauta), the process goes still further. The female of this .species (fig. 

 1.51), attains a considerable size, and is protected 1 ly an external shell. 



Fig. 150.— a Male f i jonauU a i i 11 tl 

 tained in its ^ 1 jn^ c\ st f ur t 1 



j'eiiroductiA'e lit iltt ct\l fi ) t j 



liflcil roliroduc'l ive -inn sliU r-on- 

 c.l (iiflrv JI. Ihillci); h Hetaclitd 

 nulfccux (alU'i' Kullikcr). 



The male (fig. l.'JO, a) is not more than an inch in length, is devoid 

 of a shell, and has its third left ai-m metamorjihosed. This arm is 

 developed in a cyst, and is ultimately detached from the bfidy, and 

 deposited by the male within the mantle-cavity of the female. When 

 first discovered in this position, it was described as a worm living 

 parasitically on the Argonaut, under the name of " Ilectocotylus " 

 (Gr. /lel-atoii, a hundred ; hitulos, a cup), from the suckers oi- cups 

 with which it was furnisheil. Sulisequently it was desciibed as the 

 entire male Argonaut ; and it is only recently that it has lieen proved 

 to be nothing more than one of the arms of the male, detached for 



