CLASSIFICATION OCCURRENCE AFFINITIES 



235 



The function of testis has been ascribed by Ludwig to a 

 minute granular organ between the ovaries above the rectum ; if 

 this view be correct the Gastrotricha are hermaphrodite. 



The movements of the Gastrotricha are very elegant, recalling 

 those of the long -necked Ciliate Infusoria, like Amphileptus, 

 Lacryinaria, etc., with the characteristic exception that they 

 always swim forwards ; the grace of their movements being due 

 to the bending of the head and neck on the body. Those which 

 are provided with long motile bristles like Dasydetes, alternate 

 their gliding with leaps, like the springing Eotifers. 



The Gastrotricha are divided into two sub-Orders Euichthy- 

 dina, with two pedal appendages, containing the genera Ichthy- 

 dhim Ehr., Lepidoderma Zel., Chaetonotus Ehr., and Chaetura 

 Metsch. ; and the Apodina, with no pedal appendages, com- 

 prising Dasydetes G. and Gossea Zel. 



Their geographical distribution, like that of most microscopic 

 fresh-water organisms, is cosmopolitan. Few observers have 

 enumerated the members of this group ; of their extra-temperate 

 occurrence we have only the single observations of Ehrenberg, 

 Schmarda, and Voeltzkow for Nubia, Ceylon, and Madagascar 

 respectively. 



Of the thirty-two species described, twelve are recorded by 

 A. C. Stokes from Maine and New Jersey only, besides five 

 others that occur also in Europe. In Europe nineteen species 

 are recorded, one of which, Ichthydium podura, has also been 

 found in Nubia and Ceylon. One species, Chaetonotus tabulatus 

 Schmarda, has been recorded by its author from Colombia (in 

 South America). As of the nineteen European species only 

 seven have been recorded as British, we may expect to find that 

 careful study will well repay the student in these islands. 



The affinities of this group are probably with the Turbel- 

 larians and the Nematodes ; they differ from the former in 

 the highly developed alimentary canal, and from the latter in 

 the possession of the ciliated ventral bands and wreath. The 

 general chitinisation of the skin, the primitive body-cavity, 

 the character of the alimentary canal, the ventral opening of 

 the renal canals far in front of the anus are characters shared 

 by the Nematodes, many of which possess bristles like this 

 group. But their affinity must be rather to some hypothetical 

 ancestral group than to any living Nematodes, which are destitute 



