484 TARDIGRADA 



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, w^ho published in the year 1776 

 his Opuscules de |:'7i?/szg'?<.g aiiimale et v4gMale, was the first 

 satisfactorily to describe the phenomena of the desiccation of 

 Tardigrades, though the subject of the desiccation of Eotifers, 

 Nematodes, and Infusoria had attracted much notice, since 

 Leeuwenhoek liad 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 j)i"oject, 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 C. E. Ac. Set. cxviii., 1894, p. 817. 



