630 LECTURE XXIV. 



in superimposed longitudinal layers : their anterior ends directed 

 forwards, their opposite ends often bound together by interlaced 

 filaments. The movements of the spermatophores, when liberated 

 from the sac, are truly remarkable : the smaller extremity of the 

 outer capsule, to which the spiral spring is attached, protrudes by a 

 kind of inversion, and the inner spermatic sac is drawn forwards ; 

 the action is repeated until the ejaculatory sac is extended from the 

 sheath, when there is a slight cessation of movement. It then re- 

 commences ; the sperm-sac is compressed and protruded farther ; the 

 isthmus gives way, and the spermatozoa are violently expelled, both 

 outwards and into the cavity of the external sheath. The efficient 

 cause of the movements appears to be a combination of the contrac- 

 tility of the external sheath and sperm receptacle, with the elasticity 

 of the spiral membrane, and the very rapid endosmosis through the 

 highly hygroscopic capsule. The final intention of the superaddition 

 of protecting sheaths for the semen, like those for the ova, appears to 

 relate to the safe conveyance of the spermatozoa to the ova of the 

 female, there being apparently no true intromission in the Cephalo- 

 pods ; the peculiar mechanism of the sperm-receptacles insures their 

 rupture and the dispersion of their contents after their brief transit 

 through the sea- water. The spermatozoa in the Octopods have a 

 small button-shaped head : those of the Decapods have a longer 

 cylindrical head, and a very long and slender tail. 



The spermatozoa in the receptacle of the modified cephalic arm 

 {Hectocotylus) of the male Argonaut present the same form as in the 

 Eledone. 



The cumulative experience of numerous observers, since 1839, had 

 led to the conviction that the Argonauta, with the expanded arms 

 and shell, was the female form of the species.* 



The discovery of the male has been attended with such difficulties 

 as we have seen to beset the like problem in some of the lower 

 invertebrata. 



Delia Chiaje first (1828)f figured and described an organism 

 which he found attached to the female Argonaut, and which he 

 believed to be a parasite, describing it under the name of Trichoce- 



'^ OCCXCVIII. " He had dissected every specimen of Argonaut in the present 

 collection, in which the absence of ova in the shell left the sex doubtful, and they 

 all proved to be females : this fact rendered it allowable to conjecture that the cal- 

 cifying brachial membranes, and consequently the shell, might be sexual characters 

 and peculiar to the female." " Should it be hereafter proved that the male Argo- 

 naut possessed neither a shell nor the organs for secreting it, this fact would not 

 render the hypothesis of the parasitism of the female, which does possess the calci- 

 fying membranes, at all the less tenable." p, 39. 

 ■ t OCCLXXHI. vol. ii. p. 22.'). taf. 16. fig. 4. 



