484 TARDIGRADA CHAP. 
and he is inclined to place this group at the base or near the 
base of the whole Arthropod phylum. They, however, show 
little resemblance to any of the more primitive Crustacea. 
The matter must remain to a large extent a matter of opinion, 
but there can be no doubt that the Tardigrades show more marked 
affinities to the Arthropods than to any other group of the 
animal kingdom. 
Biology.—Spallanzani, who published in the year 1776 
his Opuscules de physique animale et végétale, was the first 
satisfactorily to describe the phenomena of the desiccation of 
Tardigrades, though the subject of the desiccation of Rotifers, 
Nematodes, and Infusoria had attracted much notice, since 
Leeuwenhoek had first drawn attention to it at the very beginning 
of the century. In its natural state and in a damp atmosphere 
Tardigrades live and move and have their being like other 
animals, but if the surroundings dry up, or if one be isolated on a 
microscopic slide and slowly allowed to dry, its movements cease, 
its body shrinks, its skin becomes wrinkled, and at length it takes 
on the appearance of a much weathered grain of sand in which 
no parts are distinguishable. In this state, in which it may 
remain for years, its only vital action must be respiration, and 
this must be reduced to a minimum. When water is added it 
slowly revives, the body swells, fills out, the legs project, and 
gradually it assumes its former plump appearance. For a time 
it remains still, and is then in a very favourable condition for 
observation, but soon it begins to move and resumes its ordinary 
life which has been so curiously interrupted. 
All Tardigrades have not this peculiar power of revivification 
——anabiosis, Preyer calls it—it is confined to those species which 
live amongst moss, and the process of desiccation must be slow 
and, according to Lance,’ the animal must be protected as much 
as possible from direct contact with the air. 
According to Plate, the Tardigrada are free from parasitic 
Metazoa, which indeed could hardly find room in their minute 
bodies. They are, however, freely attacked by Bacteria and other 
lowly vegetable organisms, and these seem to flourish in the blood 
without apparently producing any deleterious effects on the host. 
Plate also records the occurrence of certain enigmatical spherical 
bodies which were found in the blood or more usually in the cells 
1 ¢. R. Ae} Sci. cxviii., 1894, p. 817. 
