PROF. 



L1II CIRCULATION ov HA&IOTIS, A GAS- 



TBKOPOD.] 



parts, which will then unite together in the veins, 

 and those veins, before they empty into the heart, 

 will again open into another cavity of the body, 

 and fill it with blood ; and from that cavity, the 

 blood is introduced by tabes into the heart. Only 

 in certain parts of the body for instance, along 

 the gills, and upon the glandular organs there 

 are regular arteries and veins (Plate LIU, fig. A)' 

 But the main portion of the blood is emptied into 

 the abdominal cavity, or emptied into another cav- 

 ity around the mouth. So that in this Haliotis, the 

 main stem arising from the heart, ends in a sack 

 in which there is the centre of the nervous system, 

 (Fig. B ) the brain of these animals, in which there 

 are the muscles of the tongue and the beginning 

 of the alimentary tube in one and the same cavity 

 in which the main mass of the blood is emptied. 

 So that the brain sv/iras in blood the muscular 

 apparatus which moves the tongue sv?ims in blood 

 and the main track of the alimentary canal, the 

 alimentary tube and the other intestines swim in 

 venous blood in the posterior cavity of the body 

 the most unexpected structure and apparatus of 

 circulation, which lias ever been observed among 

 animals. And this peculiar unconnected disposi- 

 tion of the blood system, discovered by Prof. Milne 

 Edwards, has been successively observed by him 

 and by Prof. Yalenciennea and Mr. Quatrefages, 

 in all Mollusks. In the Cuttle-Fish there is a great 

 sac in which the intestines are placed, in which 

 they move freely, which contains venous blood,and 

 giils and gland ttlarorgams, with their proper 



circumscribed with membranous tubes. What 

 be inferred from such a state of things, for the' 

 understanding of the embryonic changes which- 

 animals in general undergo ? 



\7e see every where in the beglnnias these an- 

 imals consisting of uniform cells of uniform ma- 

 terials,, And out of these uniform materials may 

 grow the most complicated structures, Fluid 

 should be circulated in the parts in order that new 

 elements should be introduced into the body u 

 And this must bs considered as brought about ic j 

 the following manner. 



Some of these cells will become loose, and when 

 loose, the fiuid, accumulated in the intercellular 

 spaces, will unite in fiakes, and those free cell& 

 swim within a liquid. This is blood. This blood 

 is nothiag but an accumulation of cells, which be- 

 come blood corpuscles, Soating in fluid within the 

 body. Let us have the cells of an embryo, and: 

 let there be a fiuid of a certain kind, and let the 

 cells and Suid all move about, and there will be ss 

 real movement of blood. First, it is only moved 

 forwards and backwards ; but channels are gradu- 

 ally formed vrithin the substance ; and thos chan- 

 nels may be lined with membrane by the coagula- 

 tion of a part of the fluid. But this may take place 

 in such a manner as to form a central cavity, which- 

 will be a heart; and to form radiating tubes, which? 

 will be arteries and veins ; or to form largs cavities* 

 around the main organs. Those large cavities 

 cannot be considered as formed in another way 

 than by the dissolution, as it were, of the embry- 

 onic substance of which they consisted primitive- 

 ly, and by the changes cf this substance into- 

 moveable blood. The moment that the embryo- 

 has come to this point of development, it is so far 

 advanced in its other changes that it takes food ; 

 it is hatched, and at that time new substance is in- 

 troduced as food into the alimentary canal. Be- 

 ing digested, the result of digestion is mixed with* 

 that blood, and so the new substances are brought 

 into tile system, to undergo the changes by which? 

 it is so complicated as finally to form a most 

 heterogeneous mass. 



That the heart must be formed from the disso'- 

 Istion, as it were, of parts of the substance of the 

 germ, is plainly shown by its peculiar position ir* 

 so many animals. In some of the Mollirsca it sur- 

 rounds the alimentary canal, forming various sacs 

 hi rruvny parts of the cavity,, And this shows- 

 plainly that there we have no regular development 

 but a sort of decomposition of the animal sub- 

 stance, which is gradually restored, by the forma- 

 tion of more and more blood, by the process of di 1 - 

 gestion. 



The classification of Mollasca which should be' 

 admitted if we base our classification upon embry- 

 onic d?ata, would differ to some e:itent from whaS 

 has been generally acknowledged. 



Generally they have been divided into six clas&- 

 es. The Cephalopoda or Cuttle-fishes, the G-astero- 

 snail-like Mollasca, the Pteropsda- 



