218 DR. CARPENTER, ON COMPARATIVE PHYSIOLOGY. 



minatini^ in au external orifice, but only red, non-ciliated, contractile 

 vessels, which cannot he traced into connection with ihe exterior, we must 

 abstain frcnu regarding the latter as a true ' sanguiferous ' sj-stem, since 

 they are obviously but an oifset (so to speak) from the 'aquiferous,' 



Fig 2. 



specially developed in this particular 

 group of animals. — The nature of the 

 vascular system in the Nematoid worms 

 has not yet been made out but there 

 appears strong ground for the belief that 

 in this order also, what has been usually 

 regarded as a sanguiferous system really 

 belongs to the ' aquiferous ' type. 



An arrangement of a different kind, 

 but one that seems referrible to the 

 ' water-vascular ' system of inferior Ar- 

 ticulata, is found in the Leech and Earth- 

 worm, which, with their allies, constitute 

 the Mcmcecious group of Annelids. In 

 the medicinal Leech, there is found on 

 either side of the posterior part of the 

 body a series of seventeen pairs of sacculi, 

 lying between the digestive casca, and 

 opening by narrow external orifices ; al- 

 though these were long ago considered 

 as respiratory organs, yet they have been 

 of late more generally regarded as organs 

 of secretion, their homological character, 

 however, as a ' water-vascular ' system, 

 appears to be demonstrated by the exist- 

 tence of intermediate forms, which con- 

 nect it with the aquiferous system of 

 Entozoa. Thus in the Branchiohdella 

 there are but two pairs of external ori- 

 fices, one at the anterior and the other at 

 the posterior extremity of the middle 

 third of the body ; each of these leads 



^ ^ to a trunk, which, after dilating into an 



tonia " hepaticum'), enlarged, showing ampulla, gives off several tortuous canals, 



the ramifications of the digestive cavity tlip Unino- r,f wliirh !« pilint-pd 1ti the 



through the whole body of the net- work tlie lining 01 wiiicu IS cuiatea. in me 

 connected with a median trunk, a, the Earthworm, again, there IS lound m each 

 mouth. segment, and on either side of the diges- 



tive tube, an enteroid vessel which returns upon itself, and which is lined 

 with cilia ; and in other Lumbricida^ these vessels have ca'cal terminations 

 in the general cavity of the body, furnished, like the water-veasols of Eo- 

 tifera, with long cilia. — Nothing similar to this has been found among the 

 branchiferous Annelida ; and it would seem as if the water-vascular system 

 were sujierseded in them by the apparatus provided for aquatic respiration, 

 which will be hereafter described. — The close resemblance which seems to 

 exist between the multiple sacculi of the Leech, and the air-sacs of the 

 lower Myriapoda, strengthens the reasons already advanced for regarding 

 the ' water-vascular ' system as the real homologue of the tracheal system 

 of Myriapods and Insects. And if the suggestion already thrown out, 

 respecting the real nature of the supposed sanguiferous system of Annelida, 

 should prove well-founded, this also would find its parallel in the closed 

 tracheal apparatus of certain Tnsect-larvte, which is connected, like it, with 

 a branchial apparatus ; the difference between the two being that the latter 



Anatomy of Fasciola' hepaticum (^Dis- 



