CEPHALOPODA. 359 



In the Octopus they are from six to eight lines in length, slightly- 

 enlarged at one extremity. Their outer tunic or capsule is elastic 

 and transparent : this contains an elongated sac, occupying the 

 larger extremity of the sheath, and filled with the minute clavate 

 spermatozoa. This sperm-sac communicates by a short narrow canal 

 or isthmus, with a second narrower or elongated sac, with highly 

 elastic parietes. From this sound sac a spiral filament is continued 

 to the small extremity of the outer sheath. In the Cuttle-fish, the 

 isthmus connecting the sperm-sac with the ejaculatory sac is longer, 

 and the coils of the spiral membrane are closer and more numerous. 

 The spermatophora, or Needhamian filaments of the Calamary are 

 remarkable for the superior size and length of the internal sac con- 

 taining the spermatozoa. 



Under every modification, the analogy of the apparatus which 

 forms the receptacle of the essential particles of the fertilising fluid, 

 with the nidamental sacs containing the ova in the opposite sex, is 

 very obvious, and this explanation of the nature of the moving 

 filaments, which has been illustrated with much accurate detail by 

 Drs. Peters and Edwards, is, without doubt, the correct view. The 

 movements of the spermatophora, 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 re- 

 peated until the ejaculatory sac is extended from the sheath, when 

 there is a slight cessation of movement. It then recommences ; 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 contractility of the 

 externa] sheath and sperm receptacle, the elasticity of the spiral 

 membrane, and the phenomena of endosmosis. 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 sperma- 

 tozoa to the ova of the female, there being apparently no true intro- 

 mission in the Cephalopoda ; 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 female organs consist in the Dibranchiate Cephalopods, as in 

 the Nautilus, of ovarium, oviduct, and superadded nidamental glands, 

 but with several modifications in the efferent part of the apparatus. 

 The ovary is always single, and the ovisacs, characterised by their 

 elliptical form and reticulate parietes, are attached to one part of its 

 cavity, as in the Nautilus. In the Cuttle-fish there is a single oviduct, 



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