64 HISTORY. 



on closely allied Polyzoa, he has fallen far short of these naturalists in tracing the intermediate 

 course of the alimentary canal. His ideas on this part of the structure seem to correspond very 

 closely with those of Rosel, and he joins with this naturalist in denying the accuracy of 

 Trembley's description of the digestive organs of the " Polype k Panache." He does not 

 admit the existence of distinct muscles, and maintains that Trembley erroneously ascribed 

 retractor muscles to his " Polype a Panache," asserting that he has mistaken for them the 

 inverted tentacular sheath. Here also, Raspail, in denying the conclusions of Trembley, 

 departs from truth ; the celebrated discoverer of the " Polype h Panache " made no such 

 mistake as that attributed to him by Raspail ; and though, as we have already seen, he 

 erroneously ascribed to the funiculus the function of a muscle, he interpreted truly as retractor 

 muscles the appearance which Raspail referred to the inverted sheath of the tentacula. 

 Raspail did not allow the cilia with which the tentacula are clothed to escape him, though he 

 strangely refers the phenomena of ciliary motion, here as well as in other cases of its occur- 

 rence, to a deceptive appearance occasioned by certain alterations in the density of the sur- 

 rounding fluid attendant on the act of respiration ; an error which we can scarcely otherwise 

 explain than by supposing it to result from the use of a microscope of very inferior powers. 

 He has seen the funiculus which Trembley mistook for a muscle, and attributes to it the 

 function of an ovary ; and he has examined the external form of the statoblasts, which he con- 

 siders to be eggs, and the structure of their investing capsule, with more detail than any pre- 

 vious observer. 



But the most singular feature in the memoir is to be found in its zoological, rather than 

 its anatomical bearing, for the author refers all the fresh-water Polyzoa to a single species, 

 believing them to be merely different stages of development and non-essential variations of his 

 " Alcyonelle fluviatile ; " an opinion which is not very far separated from that of Lichtenstein, 

 already mentioned. The doctrines of Lichtenstein and Raspail, however, made but little way ; 

 and it seems, indeed, only necessary to compare the various forms of fresh-water Polyzoa with 

 one another, to be convinced of the entire groundlessness of their positions. Raspail's memoir, 

 upon the whole, though a most elaborate one, and copiously illustrated with well-executed 

 plates, tells us very little of importance, and must, in many respects, be viewed as a retrograde 

 step in this department of zoology. 



In the same year with the appearance of Raspail's memoir, Meyen published, in the 

 'Isis,' a paper on Ahyonella* He improves, in some important points, Lamarck's definition 

 of the genus, though he retains the incorrect character which ascribes to the animal but twenty 

 or thirty tentacula. He enters also into some anatomical details, but in these we find little 

 new, while they are by no means free fi-om error. He figures more accurately than any other 

 author since the time of Trembley and Baker, the complete course of the alimentary canal, but 

 he mistakes the rectum for the stomach. The chief value, however, of Meyen's memoir is to 

 be found in the announcement of the very important fact, that the Alcj/otiella produces loco- 

 motive ciliated embryos ; he figures these, and describes them at length, but his account is in 

 some points incorrect. Raspail, in the memoir already referred to, maintains that the Lei(- 

 cophra heteroclyta, described long since by Miiller as an infusorial animalcule, is only a young 

 state of his Alcyonella fiuviatUis ; and jMeyen now confirms the opinion of Raspail, and shows 



* Meyen, Naturgeschiclite der Polypen. 'Isis,' 1828. 



