182 J. MURRAY 



on account of the comparative facility of immigration, such facts have less weight in 

 this group than in the Vertebrata. 



The further study of the Tardigrada of continental and insular areas, in which 

 cognisance would be taken of all known species, is alluring, but beyond the scope of 

 this work. 



Natural History. There is in this paper, unfortunately, too little study of pure 

 biology, or the natural history of the water-bears, except in the wide sense that the 

 form of every organism is a manifestation of life. In this sense, every trifling 

 variation of form could throw some light on the nature of the living force which 

 produces it, although we may be unable to trace its meaning. 



The conditions under which the work was done prevented much attention being 

 given to the study of living animals. Nearly all of the species were seen alive, so 

 that the material for the investigation of life-histories was available, yet we know 

 nothing as to such points as the duration of life, the time taken to grow up, the 

 changes that occur during growth, the relations of the sexes, the time required for 

 the eggs to hatch, and a host of others. 



The observation of the living animals so closely as to elucidate any of these 

 points, while fascinating to the naturalist, is too tedious, or if not tedious yet takes 

 far too long, to be compatible with the compilation of a series of reports on the 

 collections of an expedition. 



There is no suggestion made as to the meaning of the peculiarities of species in 

 their relation to their surroundings. The value of specific peculiarities to their 

 possessors is generally very obscure, so much so that in an earlier chapter dealing 

 with the Value of Species (p. 92) I have suggested that many of the specific 

 characters are " fortuitous." Fortuitous in the ordinary sense they cannot be, but 

 they may be so described in the restricted sense that they are of no definite use to 

 the species. They may have been produced by the interaction of the conditions and 

 the living force, without leading to more complete adaptation to the conditions. 

 This must be understood as applying only to certain characters, since constant 

 adaptation must have gone on as well. 



We can understand or guess at the reasons why it is advantageous to some 

 species to deposit smooth eggs in the skin at the moult, while others lay rough eggs 

 without the protection of the skin we can imagine benefits from the strange 

 simplification and encystment of water-bears. These things are obviously important, 

 whether we fully understand them or not. 



There are, however, many little peculiarities of outward form, those things which 

 supply the specific characters generally, in which it is difficult to see any advantage. 

 They may, of course, have a value which is hidden from our eyes. Such are the 

 spines and setee of Echiniscus. It seems a reasonable supposition that such spines 

 are protective : they may deter an enemy from making a meal of their possessor. 

 But there are species with the processes quite soft and weak, such as the acicular 



