v.] METAMORPHOSES OF INSECTS. 97 



Dujardin figures a specimen containing an egg, and 

 seems to have no doubt that it is a mature form. 1 



For the next descending stage we must, I think, 

 look among the Infusoria, through such genera as 

 Chaetonotus or Ichthydium. Other forms of the 

 Rotatoria, such for instance as Rattulus, and still 

 more the very remarkable species discovered in 1871 

 by Mr. Hudson, 2 and described under the name of 

 Pedalion mira, seem to lead to the Crustacea through 

 the Nauplius form. Dr. Cobbold tells me that he 

 regards the Gordii as the lowest of the Scolecida ; 

 Mr. E. Ray Lankester considers some of the Turbel- 

 laria, such genera as Mesostomum, Vortex, &c., to be 

 the lowest of existing worms ; excluding the parasitic 

 groups. Haeckel 3 also regards the Turbellaria as 

 forming the nearest approach to the Infusoria. The 

 true worms seem, however, to constitute a separate 

 branch of the animal kingdom. 



We may take, as an illustration of the lower worms, 

 the genus Prorhynchus (Fig. 59), which consists of 

 a hollow cylindrical body, containing a straight 

 simple tube, the digestive organ. 



But however simple such a creature as this may be, 

 there are others which are far less complex, far less 

 differentiated ; which therefore, on Mr. Darwin's prin- 

 ciples, may be considered still more closely to repre- 



1 See also the descriptions given by Dujardin (Ann. des Sci. Nat 

 1851, v. xv.) and Claparede (Anat. und Entwickl. der Wirbellosen 

 Thiere) of the interesting genus Echinoderes, which these two eminent 

 naturalists unite in regarding as intermediate between the Annelides and 

 the Crustacea. 



2 "On a New Rotifer." Monthly Microscopical Journal, Sept. 1871. 



3 Generelle Morphologic, vol. ii. p. 79. 



H 



