Chap. XIII.] 



HECTOCOTYLUS. 



505 



Within the mantle cavity of a female Argonaut, Cuvier 



discovered an elongated worm-like body, provided with 



a number of suckers. This he regarded as a parasite, 



and in consequence of its appearance conferred 011 it 



the distinctive name of Hectocotylus Argoiiautse. 



This " ver bien extraordinaire," as Cuvier called it, is 



nothing more than one of the arms 



of the male Argonaut, which has 



undergone a remarkable alteration, 



become greatly elongated, and had 



conveyed within it the sperinato- 



phore. When fully developed it 



breaks away from the individual 



that has produced it and makes 



its way into the mantle cavity of 



the female. 



There are various stages of 



" hectocotylisation " intermediate 



between this extreme form and 



the much more simple extrusion of 

 the spermatophore which obtains 

 in Loligo ; in the latter the fourth 

 arm on the left side has its suckers 

 rudimentary ; in Octopus it is 

 the third on the right side, and 

 in it the free end is provided with 

 a spoon-shaped plate, to which 

 the spermatophore is conveyed. 



The general lessons as to the 

 primitive origin of germinal cells may be well impressed 

 on the mind by a consideration of what obtains in the 

 Craniate Cliordata. Among the epithelial cells 

 which line the body cavity, some become, at an early 

 stage, sharply distinguished from the rest, but of these 

 germinal cells it is not at first possible to say 

 which are male and which female ; later on they 

 undergo their characteristic changes, the male cells 



Fig. 210. Spermato- 

 phore of Loligo pealii. 



a, Sheath ; b, spermatozoa ; 

 c, coiled band. (After 

 "W. K. Brooks.) 



