104 Messrs. Hancock and Embleton on the Anatomy of Eolis. 



might be called the cellular from its structure ; this it is which 

 varies so much in thickness. Next the visceral cavity there is a 

 thin stratum of longitudinal and transverse fibres ; outside of this 

 is the membranous cell-work, containing sinuses that open into 

 the trunk-veins going to the auricle. 



The muscular coating in the papillae is very delicate, and its 

 fibres wider apart than in the rest of the skin, running longi- 

 tudinally in bundles of two or three together at intervals, and 

 transversely in fewer number and less regularly, as is represented 

 in PI. IV. fig. 9 of our previous paper. 



The cell-work described as existing in the papillae communi- 

 cates freely with the system of sinuses mentioned as belonging to 

 the skin of the body, and this system again we have traced to be 

 continuous with the venous trunks leading to the auricle. 



Under the compressor of the microscope we have seen, in the 

 cellular layer of the papillae, the blood move backwards and for- 

 wards to and from the base of the papillae and into the skin, in 

 obedience to the contractions of the body and of the papillary 

 walls ; but we believe, that if the animal were at rest and quite 

 free, the action of the heart would also cause similar motions 

 in the normal way. We look upon the contractions of the gene- 

 ral integument and of the papillae to be only accessory, not essen- 

 tial, to the perfect circulation of the blood. 



Now the whole or nearly the whole of the blood that passes to 

 the auricle of the heart comes, as we have shown, in the section 

 on the circulatory organs, directly from the skin, and as we 

 know that the blood thus circulating in the skin and papillae is 

 separated from the oxygenated water of the surrounding sea by 

 a very thin layer, in the papillae by an exceedingly delicate mem- 

 brane, we have little hesitation in sajang, that it is in the papillae 

 essentially, and in the rest of the skin secondarily, that the func- 

 tion of arterialization of the blood is carried on previously to the 

 return of that fluid to the heart. 



EXPLANATION OF PLATES IIL and IV. 

 Plate IIL 



Fig. 1. General view of the generative organs oi E.papillosa partially drawn 

 asunder: a, sac of penis retracted into body; b, female channel; 

 cc, testis; d, ovarium; e, oviduct; /, dilated portion of ditto; 

 e', continuation of ditto towards spermatheca duct;^^, transpa- 

 rent portion of mucus-gland ; g' g', opake portion of ditto; h, sper- 

 matheca ; i, its duct ; j, accessory glandule ; k, confluence of testis 

 and oviduct. 



Fig. 2. Same organs more fully displayed : a, sac of penis; a', male orifice; 

 b, female channel ; b', female orifice; cc, portions of testis ; e, ovi- 

 duct ; /, dilated portion of same ; e', continuation of ditto to testis ; 

 gg, pellucid portion of mucus-gland ; g', granular portion of ditto ; 

 h, spermatheca ; i, its duct ; jj, accessory glands ; k, sudden angle 



