ENCYSTMENT OF TARDIGRADA. 847 



hatched with only two claws on each leg, while the adults have four. They have some- 

 times also fewer or shorter setse or other processes. They attain the four claws very 

 early, probably at the first moult, and while still quite small. Unlike the Acarina, the 

 larvae have the full adult complement of limbs. 



I have seen an individual of E. granulatus, Doy., which had been unable to completely 

 throw off the old skin at the moult, and it remained adherent till the next moult. It 

 was thus possible to compare three stages of the same individual. In these two moults 

 there was very little increase in size, but some of the processes elongated considerably, 

 and the straight spines on the outer claws increased in number. 



There must in this case have been at least three moults — the one when it ceased to 

 be a larva, and the two actually observed ; but as the animal when first seen was very 

 much larger than the larva, it is certain that there must have been one or more 

 intermediate moults. 



The rigid skin of Echiniscus may require to be more frequently cast than the softer 

 skin of Macrobiotics, and Schultze may be right about the two moults of M. hufelandi. 



The female does not ordinarily die after casting her skin and laying her eggs. One 

 species at least carries the eggs about till they are hatched, and continues to live for 

 some time after, though I have never been able to keep an individual under observation 

 till a second lot of eggs was developed. On the whole, I am inclined to think that 

 even after maturity the skin is changed more than once, and successive clutches of 

 eggs are laid. 



During encystment some species cast off at least three and possibly four coats, but 

 these may not be true skins. 



Systematic Position of Tardigrada. 



The systematic position of the Tardigrada has given rise to much controversy. The 

 only point on which there is general agreement is that they are Arthropoda, Dujardin 

 alone among prominent naturalists assigning them a lower place — with the Rotifers in 

 his class of the Systolides — an opinion which he afterwards modified. 



It is not intended here to enter into the whole question, but merely to give a sketch 

 of the history of the controversy, and to enquire whether the phenomena of encystment 

 bring it any nearer settlement. 



0. F. Muller (24) in 1785 first gave a scientific name to a Tardigrade, Acarus 

 ursellus, which he thus included among the Acari. Muller's view is accepted by 

 Gmelin, 1788, (13), Dutrochet, 1837 (9), Kauffmann, 1851 (19), etc. Schrank, 1804 

 (33), also put them near the Acari, in his Insecta Aptera, between Pulex and Acarus. 



They were regarded as true Insects by Dutrochet in his earlier work, 1812 (8), 

 Blainville, 1826 (2), etc. 



They were reckoned among Crustacea by Nitzsch, 1820 (28), Schultz, 1834 (34), 

 Ehrenberg, 1834 (10), Perty, 1834 (29), etc. 



