2b8 



NATURAL HISTORY. 



SOME DOUBTFUL FORMS. 



Before we close our account of the great group of Arthropods, we must 

 mention, at least by name, some forms concerning whose affinities natural- 

 ists are in doubt. It is easy enough to find them assigned to some position 

 in the cut-and-dried systems of books ; but the trouble is, they will not fit 

 where they should. 



First of these comes a worm-like form, — Peripatus by name, — which 

 every one regarded as a true worm, until Professor Moseley showed that it 

 breathed in much the same manner as do the higher insects. Immediately 

 was this discovery made, the form took a very high rank from a scientific 

 standpoint ; for it had so many peculiar features that it was at once 

 thought that here was the key to many deep problems concerning the 

 exact way in which the insects arose. Alas for these hopes ! Peripatus 

 has not solved the question it was expected to solve ; and in the writer's 

 opinion it has little or nothing to do with it, but possibly belongs among 

 the worms, near where it was formerly assigned. Still, the study directed 

 in this way has been of great value, for by it much light has been thrown 

 upon many other questions concerning which naturalists were all at sea. 



A second group are the water-bears, — minute aquatic animals with 

 eight legs, and quite a bear-like appearance, which occasionally appear in 

 the collections of microscopists. Usually they are placed among the 

 spiders, merely because they have eight legs, but beyond this there is but 

 little to warrant such assignment. Specimens are rare, and should be 

 sought in the wet moss of swamps, where they occur along with the amoeba, 

 described in the early pages of this volume. 



The last forms to be mentioned are the sea-spiders, which are found in 

 abundance in every sea. They are small-bodied, slender-legged forms, 

 which wander about over the hydroids in a lazy manner. Their young live 

 as parasites in the hydroids, forming swellings where they occur. Like 

 the last they are usually classed with the spiders, and for the same reason ; 

 but this step is one of doubtful propriety. Most of these forms along our 

 shores are small ; but the deep-sea dredgings have revealed specimens of 

 enormous size, some measuring nearly two feet across the extended legs, 

 and the body so small that it appears almost like a knot tying the string- 

 like legs together. 



