334 Dr. T. Williams on the Mechanism of Aquatic 



which entitles them to rank near the Echiuoderms. The cavity 

 of the body is capacious ; it is filled with a fluid which is sustained 

 in motion by provisions expi'essly designed for this purpose. 

 Vibratile ' tags/ accurately described by Ehrenberg and Dal- 

 rymple^ aided by ordinary cilia on the external surface of the 

 digestive canal, are well fitted for this office. The cavity ex- 

 ternal to the viscera is filled with a fluid, remarked by all ob- 

 servers, but specially described by none. Its nutritive character 

 may be confidently inferred : 1st positively, from its anatomical 

 locale ; 2ud negatively, from the absence of every other fluid. 

 ' Tags ' and ' cilia ' cannot aerate a vital fluid ; they can only set 

 it and maintain it in motion. Confusion has brooded over this 

 simple point. Only the thin structure forming the exterior en- 

 closure of the body intervenes between the fluid of the visceral 

 cavity and the surrounding element. Thus is the former sub- 

 mitted to the influence of the aei'ating agent*. 



Entozoa. — Mystery has long enshrouded the natural history 

 of the Entozoon. Living in situations bej'ond the access of the 

 atmosphere, and totally uncomprehended in the real character 

 and distribution of its fluids, the mechanism of the respiratory 

 process has proved only the arena for conjecture and speculation 

 as erroneous as various and contradictory. M. E. Blanchard has 

 long misled the helminthologists of Europe. In the Cestoid and 

 Trematoid Entozoa he has pictorially represented a blood-proper 

 system of extreme complexity and development. He has figured 

 with elaborate minuteness that which has no existence in na- 

 ture t- He has confounded an apparatus of irregular, ramifying 



* See the excellent Art. Ratifera, by Dr. Lankester, in Cyclop. Anat. and 

 Phys. " Contributions to the Anatomy and Physiology of the Rotifera," 

 by Mr. Huxley in Micros. Journal. Annales des Sciences, 1851, Art. Laci- 

 nularia, par M. Udeken. Leydig on Lacinularia socialis, in Siebold and 

 Kolhker's Zeitsehrift, Feb. 1852. 



t The author would desire to speak with respect of the researches of 

 M. E. Blanchard on the Entozoa. His memoirs on this subject enrich the 

 pages of the ' Annales des Sciences Natiu-elles ' for the years 1847, 1848 and 

 1849. His illustrative figures, which are copied into Crochard's edition of 

 the ' Regne Animal,' executed in the highest style of French art, are de- 

 signed to display the true-blood system of the Cestoid and Trematoid 

 worms. With reference to the latter order he remarks : — " Au moyen de 

 mes injections, je me suis assure qu'il existait chez ces animaux un appareil 

 de vaisseaux a parois propres, se ramifiant dans toute I'etendue du coi-ps. 

 On ne distingue ici ni veines, ni arteres proprement ditcs ; les deux fonctions 

 paraissent appartenir aux memes vaisseaux ! " — Is it not extraordinary that 

 such a distiuguished physiologist as M. E. Blanchard should oiFer such a defi- 

 nition of any apparatus designed to circulate true blood ? where in the ani- 

 mal kingdom could a parallel to such a system be indicated ? — " Nous le 

 voyons consister en un ou plusieurs vaisseaux principaux, oifrant de nom- 

 breuses ramifications s'anastomosant sur une infinite de points ; en sorte 



