v.] METAMORPHOSES OF INSECTS. 93 



the water-inhabiting and water-breathing Crustacea 

 must be regarded as the original stem from which 

 the other terrestrial classes, with their tracheal respi- 

 ration, have branched off." Haeckel, moreover, is of 

 the opinion that the Tracheata are developed from 

 the Crustacea, and probably from the Zoepoda. 

 For my own part, though I feel very great diffidence 

 in expressing an opinion at variance with that of 

 such high authorities, I am rather disposed to suggest 

 that the Campodea type may possibly have been 

 derived from a less highly developed one, resembling 

 the modern Tardigrade, 1 a (Fig. 56) smaller and much 



FIG. 56, Tardigrade (after Dujardin). 



less highly organized being than Campodea. It pos- 

 sesses two eyes, three anterior pairs of legs, and one 

 at the posterior end of the body, giving it a curious 

 resemblance to some Lepidopterous larvae. 



These legs, however, as will be seen, are reduced 

 to mere projections. But for them, the Tardigrada 



1 A still nearer approach is afforded by the genus Peripatus, which 

 since the above was written has been carefully described, especially by 

 Moseley and Hutton. There are several species, scattered over the 

 southern hemisphere. In general appearance they look like a link 

 between a caterpillar and a centipede. They have a pair of antennas, 

 two pairs of jaws, and (according to the species) from fourteen to 

 thirty-three pairs of legs. They breathe by means of tracheae, which 

 open diffusely all over the body. 



