158 Anatomy of Doris. 



cond, the portal, in which venous blood from the system is 

 driven by a special heart to the renal and hepatic organs, and 

 probably to the ovarium, where it escapes doubly venous, 

 with the rest of the blood which has been supplied to these 

 organs from the aorta, and which is therefore only singly 

 venous, to the branchiae : third, the branchial circulation, in 

 whicli flows only the more deteriorated blood, brought by the 

 hepatic vein, but in which also that blood undergoes the 

 highest degree of purification capable of being effected in the 

 economy, namely, in the special organ of respiration. This 

 triple circulation has not yet, as far as the authors are aware, 

 been described as existing in the molluscan sub-kingdom. 

 From the fact of the blood in Doris being returned to the 

 heart in a state'of partial aeration, it is clear, they say, that 

 this animal is, in this respect, on a par with the higher crus- 

 taceans ; and from the blood arriving at the heart in the 

 same condition, according to the researches of Garner and 

 Milne-Edwards, in Ostrea and Pinna, the Great Triton of the 

 Mediterranean, Haliotis, Patella, and Helix, it can scarcely 

 be doubted that this arrangement will be found throughout 

 the Mollusca. 



From a consideration of the facts cited in the paper, it may 

 be deduced that the skin or mantle is, in the mollusca, the 

 fundamental organ of respiration, and that a portion of that 

 envelope becomes evolved into a specialty, as we trace up- 

 wards the development of the respiratory powers. 



Upon the dorsal aspect of the liver mass is a branched 

 cavity, that of the renal organ, lined with a spongy tissue, and 

 opening externally at the small orifice near the anus. 



Organs of Innervation. — These are in two divisions, — one 

 corresponding to the cerebro-spinal division, the other to the 

 sympathetic or ganglionic system of the vertebrata. The 

 existence of the latter, it is stated, is now, for the first time, 

 fully established. The centres of the first system are seven 

 pairs and a half of ganglia. Of the seven pairs, five are 

 supra-oesophageal, two infra-cesophageal ; the single ganglion 

 belongs to the right side ; and has been named visceral. There 

 are three nervous collars around the oesophagus, one of which 

 connects the infra with the supra-oesophageal. The total 



