INTRODUCTION 



TARDIGRADA. were collected not only in the Antarctic, but in all other countries 

 visited by the Expedition in the course of the voyage round the world. These were 

 New Zealand, the Macquarie Islands, Australia, Fiji, Hawaii, and Canada. A brief 

 visit was paid to South Africa, and some moss was collected on Table Mountain by 

 Drs. Mackay and Michell, but though animals of other sorts were plentiful enough, 

 no Tardigrada were found. 



The great majority of the Tardigrada obtained were of the k'nds which live among 

 moss. These everywhere over the world greatly exceed in numbers the true water- 

 dwellers. All, of course, are aquatic animals, in the sense that they must have at least 

 a film of water to support their active life, but the dwellers among moss have to 

 endure frequent and often long-continued desiccation, while the others live in ponds 

 and other waters of a more permanent sort. Though a number of species are common 

 to both habitats, there is no doubt that most are confined to one or other. The moss- 

 dwellers are adapted to withstand desiccation, the others may be equally so, but they 

 are rarely exposed to tests of their powers. By desiccation it is not meant that the 

 animals can endure the loss of all moisture from their bodies, but that they can live 

 when completely deprived of the external watery element. When so deprived they 

 are dormant, and if any physiological change goes on, it must be excessively slow. 



Only some half-dozen species are well recognised as habitual pond-dwellers, 

 though in Scotland a good many others are frequently found in ponds, lakes, and 

 rivers. 



It was only in New Zealand, Australia, and the Antarctic that there was much 

 opportunity of looking for the purely aquatic kinds. In those countries which were 

 only visited in passing there was no available method of collecting except by taking 

 dry moss to be examined afterwards at leisure. Nothing could exceed the facility of 

 this mode of collecting. The moss is preferably gathered dry ; the animals have 

 already become dormant in the natural course, and nothing is required for the 

 examination afterwards, but to moisten the moss, when in half an hour or so the 

 animals are found to be active. They will not live indefinitely, but for a year at 

 least they can quickly be revived when wanted, and some have been kept for a 

 number of years alive. 



In this paper, after some introductory paragraphs dealing with structure, nomen- 



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