14 Prof. KoLLiKER on the Structure of 



was I able to discover vessels, which, from a connexion with the aorta, would 

 appear to be the arteries of the body. 



With regard to minute structure, the capillaries are formed by one single, 

 delicate membrane provided with nuclei ; the larger vessels have in addition 

 to this membrane a layer of muscular fibres more or less thick. 



e. Nervous System and Organs of Sensation. 



The only fact which I can furnish with regard to the nervous system is, 

 that there exists a small nerve running alongside the intestine, which is pro- 

 vided, as far as I have observed, with one ganglion containing nucleated cells. 

 This nerve is included in a sheath of cellular tissue, and gives off branches to 

 the intestine. 



I was equally unfortunate in my endeavours to discover the organs of sen- 

 sation, being, after the most careful observation, unable to find organs either 

 of sight or hearing or tentacles. 



f. Organs of Generation. 



All the specimens which I saw were males. The testicle is formed by an 

 extremely long, small and tortuous tube, which fills nearly the whole of the sac 

 above mentioned, and can easily be perceived in the living animal through the 

 pellucid membrane of the sac. The vas deferens is provided with a strong 

 muscular layer, and has its posterior part included in the oval sac ; whilst 

 the anterior part, which is 'narrower, runs through the middle of the penis, 

 and opens at its extremity by a small orifice. The semen, when taken from 

 the living animal, presents the appearance of a silk thread. It consists of 

 innumerable spermatozoa, which have the same size and form as those in 

 Octopus vulgaris, and which originate from small cells filling the end of the 

 testicle. 



Description of the Hectocotyle of Argonauta Argo. 



Delle Chiaje in his memoirs has given a very unsatisfactory figure and de- 

 scription of this animal, which he has named Trichocephalus acetabularis. 

 Many years later Costa found specimens of the same animal, and described 

 it also imperfectly, though better than Delle Chiaje, in the 16th volume of the 



