216 DR. CARPENTER, ON COMPARATIVE PHYSIOLOGY. 



evidently taken the greatest pains to bring it up to the 

 standard of knowledge of the present day. We are glad to 

 find no indications that the author is inclined to rest on his 

 wide-spread reputation and the popularity of his works, but 

 that he has in every department laboured to give the fairest 

 possible exposition of his science. The principal additions 

 and alterations in this volume, as we learn from the author's 

 preface, occur in relation to the water-vascular system of 

 some animals, and the sexuality of Cryptogamic plants. We 

 subjoin Dr. Carpenter's account of the water-vasculiir system, 

 as its existence and peculiarities have been determined by 

 the aid of the microscope. 



It is among the Vermiform members of the articulated series, that Ave 

 find the ' water-vascular ' system acquiring its highest development. But 

 it will be desirable first to study it under the simpler form it presents in 

 the Botifera, which have no rudiment of a sanguiferous system, the chyl- 

 aqueous fluid of the general cavity of the body being the medium alike 

 for conveying nutriment to the solid tissues, and for effecting respiratory 

 changes in tliem. On either side of the body of these animals, there is 

 usually found a long flexuous tube, which extends from a contractile vesicle 

 (common to both) that opens into the cloaca, towards the anterior region 

 of the body, where it frequently siibdivides into branches, one of which 

 may arch over towards the opposite side, and inosculate with a correspond- 

 ing branch from its tube. Attached to each of these tubes are a number 

 of peculiar organs (usually from two to eight on each side) in Avhich a 

 trembling movement is seen, very like that of a flickering flame ; these 

 appear to be pear-shaped sacs, attached by hollow stalks to the main tube, 

 having a long cilium in the interior of each, attached by one extremity to 

 the interior of the sac, and vibrating with a quick undulatory motion in 

 its cavity ; and there can be no doubt that their purpose is to keep-up a 

 continual movement in the contents of the aquiferous tubes. — Similar 

 lateral vessels, furnished internally mth vibratile cilia, and often ramify- 

 ing more minutely (especially in the head and anterior part of the body) 

 are found in many of that group of Vermiform animals, clothed over the 

 whole surface of their bodies with cilia, to which the designation Turhel- 

 laria has of late been given. These vessels have been commonly regarded 

 as sanguiferous ; and it is certain that the fluid which they contain is 

 sometimes coloured, like the (so-called) blood of Annelida ; but it is 

 certain, also, that they have usually, probably always, external orifices, 

 these being sometimes numerous. In Nais, instead of actually opening 

 into the cloaca, one set of them comes into close relation to the rectum, 

 the interior of which is richly ciliated ; thus reminding us of the parallel 

 distribution of the tracheal system in the larva3 of Libellulidce. In fact, 

 it seems not improbable that the ' water- vascular ' system of the lower 

 Articulata (which are all aquatic) is the homologue of the tracheal system 

 of the air-breathing Myriapods and Insects ; and that, where it does not 

 convey water directly introduced from without, the fluid which it contains 

 is specially subservient to respiration, establishing a communication be- 

 tween the aerating surface and the tissues of the body generally. There is 

 an almost complete absence among the TurheJlarice of any more special 

 respiratory organs. The whole tegiunen of the body, being soft and 

 clothed with cilia, is probably subservient to this function ; but there are 



