20 LAWSON, ON LIMAX MAXIMUS. 
isted, that is to say, a complete series of channels, by which 
the nutrient fluid was conveyed from the propelling organ to 
the various regions of the body, and returned to the heart. 
Milne Edwards* has done much to correct the errors of the 
earlier investigators; but as his observations do not extend 
to Limax, and since the latter genus and that of Helix, the 
course of whose circulation has been traced, are so widely 
distinct anatomically, the mode in which the blood is car- 
ried to and from the heart and pulmonary organs of the slug, 
has not as yet been distinctly explained. I have most care- 
fully pursued the examination of this subject, occasionally 
with the assistance of injections prepared with new milk, and 
the result has been the adoption of the following view. The 
blood, having been expelled from the heart, travels through 
the short aorta and its two divisions, in this way reaching the 
head, reproductive organs, intestinal sanal, and liver, and, 
having arrived at the terminal ramifications of the arterial 
vessels, is poured through their open extremities into the ab- 
dominal and sub-thoracic cavities, thus bathing the external 
parictes of the viscera; these cavities are continuous, and 
clothed without by the general integument, in whose walls 
the various channels are tunneled. Now, the veins begin as 
minute apertures,t which admit the blood hitherto contained 
in the visceral chamber, allowing it to pass into their smaller 
branches ; from these it then flows into the larger vessels, 
and is finally transmitted by the great pulmonary vein of 
each side, to the respiratory sacs. It is here that difficulty 
has been invariably experienced, in tracing the channels by 
which the blood travels to the heart, some contending that a 
portion flowed to the so-called kidney, whilst the remainder 
was brought on to the heart by a large pulmonary vessel ; 
others that the blood was here poured into a sinus or lacuna. 
Both these ideas I conceive to be erroneous, the more so as 
I have been unable, after the closest scrutiny, to detect any 
single pulmonary vessel which might of itself convey the 
blood to the heart; and besides that, the relations and cha- 
racter of the guasi kidney have been most certainly misin- 
terpreted. The circulation in this locality is most complete 
and peculiar, and can be seen with more or less distinctness 
by removing the mantle, and membrane of the shell-sac. 
When this has been done, it will be observed that the blood 
travels in the direction I have endeavoured to indicate 
diagramatically (fig. 6), viz., having been poured by the 
* © Ann. des Sci. nat.,’ viii, 1847. 
+ The merit of this discovery is, I believe, due to Cuvier; vide for 
Aplysia, ‘Ann. du Mus. d’histoire nat.,’ ii, p. 299. 
