Circulation of Helix pomatia. 7 



injection is thrown in and allowed to cool, some trace of these 

 communications ought to be found. 



If my experiments are correct, the course of the blood after 

 leaving the heart will be as follows : — From the artery it passes 

 into a plexus of capillaries, which are richly spread over the 

 whole of the body, and from them it is collected into veins with 

 distinct walls, which return the whole of it to a large sinus by 

 the side of the rectum (PI. I. fig. 2 c). From this sinus the 

 blood passes, first, into the capillaries of the pulmonary sac, 

 which is situated between the rectum and kidney (fig. 2 d), and, 

 lastly, runs forward and round into the whole of the anterior 

 portion of the sac, the whole of the venous blood being thus 

 aerated before returning to the heart. The arterial blood which 

 is collected from the posterior narrow slip of pulmonary sac 

 passes through the kidney (fig. 2 e) before it reaches the pulmo- 

 nary vein. The kidney, therefore, is supplied with blood which 

 has been previously aerated in the pulmonary capillaries ; but 

 the whole of the venous blood does not pass through it*. 



I think it extremely probable that, with improved injection- 

 fluids and injecting-apparatus, and by paying attention to the 

 state of the animal before the injection is begun, a closed system 

 of vessels will be found in other Gasteropoda. Messrs. Hancock 

 and Embleton, after describing the arterial and venous systems 

 of the Eolis, and the mode of communication between these 

 systems, go on to remarkf, " We cannot undertake to say 

 whether they end by closed extremities, or whether they have 

 open mouths which communicate with lacunae or sinuses in the 

 intervisceral spaces, or with those in the skin. The lacunae in 

 the viscera we have not been able to make out by dissection, and 

 have not made use of injections on account of the great difficulty 

 of injecting such small animals.^' Also, in their account of the 

 vascular system of the Nudibranchiate Mollusca J, " The parietal 

 or hepatic system is probably provided with a complete system 

 of capillaries.'^ 



EXPLANATION OF PLATE I. 



The arterial system of Helix pomatia, from a photograph by Messrs. 

 Wheeler & Day, Oxford. 



Fig. 1. The foot has been placed downwards, and the dissection made 



* Milne-Edwards says that the whole of the venous blood is not obliged 

 to traverse the pulmonary chamber before reaching the heart, part of it 

 being carried by a system of canals and vessels to the kidney (Lemons sur 

 la Physiologie et TAnatoraie Coraparee, vol. iii. p. 148). Prof. Lawson says 

 that a capillary system does not exist in Limax maximiis (Quart. Journ. 

 Microscopical Science, January 1863). 



t Anatomy of Eolis, Ann. Nat. Hist. (1848), vol. i. p. 100. 



X Alder and Hancock's * Nudibranchiate MoUusca,' vii. p. 15. 



