230 FOURTH REPORT — 1834. 



Infusoria can be preserved as distinct classes. It should be 

 Slated, however, that he has embraced some peculiar vievps re- 

 specting the systematic distribution of animals, of which it is 

 impossible to give any detailed account here. I may also allude 

 to a curious memoir by Duges in the Ann. des Set. for 1832*, 

 as affording fresh suspicion that the Entozoa do not form a 

 natural class of themselves to the exclusion of other animals. 

 He describes a new and veiy singular genus found free in water 

 amongst duckweed, which appears to be closely allied to the 

 ToEuicB and Bntliriocephali. It is small, but has its body di- 

 vided into segments like those animals, these segments being of 

 a similar form, and varying in number from four to eight. Duges 

 thinks it not improbable that this may have been the supposed 

 Tcenia which Linnaeus is said to have met with free in water. 

 He gives it the name of Catenula Lemnce. 



The PlanaricE, again, present us witli a group of animals not 

 parasitic, which are now universally admitted amongst the Paren- 

 chymatous Worms, and considered as belonging to the Tremadota 

 of Rudolphi. Cuvier iuf^ecd (as Lamarck and others had already 

 done) assigned them this place in the first editi(m of the R^gne 

 Animal, but it was not without doubts as to their true situation. 

 These doubts are now quite removed by the researches of Dr. 

 Baer and M. Duges, both of whom have investigated the struc- 

 ture of these animals, the former in the memoirs before alluded 

 to, the latter in the Ann. des Sci. for 1828 and 1830f . The 

 result is, that neither of these observers has been able to detect 

 any muscular, or ganglionic nervous system ; and the latter thinks 

 that it is the absence of these systems principally which serves 

 to separate them from the HirudinidcE, with Avhich they have 

 been so often classed. At the same time, Duges points out seve- 

 ral respects in which they clearly approach the group just men- 

 tioned. It may be added, that Duges has proposed in his me- 

 moir to raise the Planaria; to the rank of a family, in M^hich 

 he particularizes three distinct genera. These he has charac- 

 terized from the structure of the digestive organs, and the situa- 

 tion as well as number of the orifices. 



As there are some groups which, though«o# parasitic, require to 

 be associated with the Entozoa, there are others which are para- 

 sitic, and which many have arranged with these animals, but of 

 which the true situation is extremely doubtful. Such are the Ler- 

 ?««<:e,presentingsuch evident affinities to the Siphonostomous En- 



* torn. xxvi. p. 198. 



t I may also allude to two papers by Dr. Rawlins Johnson in the Phil. 

 Trans, for 1822 and 182.5, containing the result of some inquiries into the power 

 of reproduction possessed by these animals. This subject, however, had been 

 previously investigated by Mr. Dalyell in his interesting memoir on the Plajia- 

 riiE, published at Edinburgh in 1814. 



