CHAPTER XIX 



TARDIGKADA 



OCCURRENCE — ECDYSIS — STRUCTURE — DEVELOPMENT — AFFINITIES 



BIOLOGY DESICCATION PARASITES SYSTEMATIC 



The animals dealt with in this chapter lead obscure lives, remote 

 from the world, and few but the specialist have any first-hand 

 acquaintance with them. Structurally they are thought to show 

 affinities with the Arachnida, but their connexion with this 

 Phylum is at best a remote one. 



Tardigrades are amongst the most minute multicellular 

 animals which exist, and their small size — averaoino- from 

 ^ to 1 mm. in length — and retiring habits render them very 

 inconspicuous, so that as a rule they are overlooked ; yet Max 

 Schultze -^ asserts that without any doubt they are the most 

 widely distributed of all segmented animals. They are found 

 amongst moss, etc., growing in gutters, on roofs, trees or in 

 ditches, and in such numbers that .Schultze states that almost any 

 piece of moss the size of a pea will, if closely examined, yield 

 some members of this group, but they are very difficult to see. 

 The genus Macrohiotv.s especially affects the roots of moss growing 

 on stones and old walls. 31. macronyx lives entirely in fresh 

 water, and Lydella dujardini and Echiniscoides siyismundi are 

 marine ; all other species are practically terrestrial, though in- 

 habiting very damp places. 



In searching amongst the heather of the Scotch moors for 

 the ova and embryos of the Nematodes which infest the ali- 

 mentary canal of the grouse, I have recently adopted a method 

 not, as far as I am aware, in use before, and one which in every 

 1 Arch, iiiikr. Anat. Bd. i., 1865, p. 428. 

 477 



