218 CIRCULATION IN MOLLUSCA. 



with the alimentary canal, but I find no mention made rela- 

 tive to its condition in this cavity, whether stagnant or 

 fluent, or how long it tarries there. It in some way, how- 

 ever, passes from it into other vessels, which have the office 

 assigned them of subjecting this blood to the vivifying action 

 of the air, and then to return it to the aortic heart or 

 centre whence it started on its course. It is the same essen- 

 tially in other Gasteropods. In the Cephalopods the venous 

 system is still more perfected, yet without being made com- 

 plete, for the visceral cavity continues to hold the place of a 

 portion of the venous system. In the octopod Cephalo- 

 pods the venous circulation is semi-lacunose in the abdomen 

 as well as in the head; but in the Cephalopods with ten 

 arms or tentacula, the system is entirely vascular in every 

 part of the abdomen, and the lacunose portion of the circu- 

 lating circle is found only in the head, where the blood is 

 effused into a sinus containing the upper portion of the 

 alimentary canal. Incompleteness then, or rather an inter- 

 ruption to the even and continuous flow of the blood in 

 closed vessels in some part of its course, is the law with the 

 mollusca, as it is, indeed, with the Crustacea and inverte- 

 brate animals in general. * And this discovery, pronounced 

 by Professor Owen to be the greatest made in the physio- 

 logy of these animals of late years, reduces many of the 

 so-called anomalous structures noticed in our previous re- 

 view to the normal rule. They are reservoirs into which the 

 veins open by wide and unvalved apertures, and pour the 

 refluent blood. The aquiferous system of Delle Chiaje is 

 of the same character, and forms the lacunose portion of the 

 venous circle.-)- But while we may admit this, I must at 

 the same time guard against your rejection of the office 

 assigned to this organization in my letter on the aquiferous 

 system, for the turgescence of the body, or its members, 

 from the filling of the canals whether from without by 

 water, or from within by blood, must exert the same influ- 

 ence over locomotion. In the case of the Gasteropods, 



* Thus every thing concurs to prove the existence of a semi-vascular, 

 semi-lacunose circulation in, the mollusca, as well as in the Crustacea and 

 arachnides ; and if we wished to express by a general formula all the facts 

 already ascertained that prove it, we might say that in all animals with 

 white blood, the nutrient fluids are not enclosed in a closed vascular appa- 

 ratus, but circulate more or less rapidly in a system of cavities formed in 

 whole or in part by the interstices which are left between the different or- 

 gans. MILNE-EDWARDS, Ann. des Sc. Nat. (1845), iii. 314. 



f Recherches Zoologiques faites pendant un Voyage sur les Cotes de la 

 Sicile, par M. Milne-Edwards. Observations sur la Circulation. Ann. 

 des Sc. Nat. 3 ser. iii. (1845) p. 257. Nouvelles Observations sur la Con- 

 stitution de 1'Appareil circulatoire chez les Mollusques ; par MM. Milne- 



