CHAPTER XIX 
TARDIGRADA 
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—averaging 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 Macrobiotus especially affects the roots of moss growing 
on stones and old walls. JL macronyx lives entirely in fresh 
water, and Lydella dwjardini and Echiniscoides sigismundi 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. mikr. Anat. Bd. i., 1865, p. 428. 
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