258 Analytical Notices of Books. 



down by the authour, the chaotic mass of animals confounded by natu- 

 rahsts under the common name of Entozoa. It consists of seven distinct 

 memoirs, the first six of which have for their object to illustrate particu- 

 lar individuals or groups, while the last is intended to convey a summary 

 idea of the authour's opinions with regard to the affinities and classifica- 

 tion of the lower animals. 



The first of the series relates to a new genus of these animals, inha- 

 biting the various species of fresh-water muscles (Anodonta and UnioJ 

 and belonging to Rudolphi's order Trematodce. It is described by Dr. 

 von Baer under the name of Aspidogaster, and with the following cha- 

 racters : — " Ore et ano oppositis, lamina clathrata sub ventre ;" the latter 

 of which, he observes, is fully sufficient to distinguish it from every other 

 genus of intestinal worms, the former being only added because he is 

 convinced that naturalists will ere long cease to consider these worms as 

 forming a distinct and separate class. Of the minuteness with which the 

 single species has been investigated, some judgment may be formed from 

 the fact that the mere technical description occupies more than fourteen 

 pages. 



The second memoir completes the series of the authour's observations 

 on the parasites of the fresh-water Muscles, and contains the history of 

 a curious species of Distoma, which in consequence of its singular 

 structure he names duplicatum; and of a new and very remarkable 

 genus, approaching to the Infusoria, and even in some respects to the 

 lower forms of vegetable organisation, to which, by an apt comparison, 

 he assigns the designation of Bucephalus, the species described being so 

 excessively variable as to merit par excellence the epithet of poly- 

 morphus. It furnishes moreover a brief indication of a species of 

 Filar la; a notice of a new Hydrachna, H. concharum ; and some 

 interesting observations relative to a " chaotic swarm," composed of 

 living creatures of various forms and degrees of organisation, which 

 appears to pervade in a greater or less degree every part of the animals 

 xmder consideration. 



In his third memoir the authour illustrates in a similar manner the 

 history of the parasites which infest the fresh-water univalves, and more 

 particularly the Paludin<e and Limneee. These consist of several species 

 of Distoma; of a new genus, Chcetogaster, approaching very nearly 

 to the JSfais of authours, and comprehending, besides the animals now 



