850 MR JAMES MURRAY ON 



aquatic species, living in shallow still water, and in the place where it was studied the 

 cysts remained in the moss where they were formed, under the ice. 



Megnin believed that the change of a nymph into a hypopus was caused by un- 

 favourable conditions. Michael thought it had no connection with unfavourable 

 conditions. 



With regard to the Tardigrada, I believe the evidence goes to show that the encyst- 

 ment is induced by unfavourable conditions. It may be the low temperature which is 

 the unfavourable condition for aquatic forms, and the drying of the moss in the case 

 of the terrestrial forms. The encystment of Protozoa appears to be frequently induced 

 by adverse circumstances, though it may have other causes. 



Further investigation will be necessary before it will be possible to draw any more 

 definite conclusions as to the meaning of the encystment of Tardigrada. 



Note on M. macronyx, M. dispar, and Related Species. 



M. macronyx and M. dispar appear to have much in common, although, if the 

 two modes of disposing of the eggs really differentiate natural groups, they would be 

 placed in different sections of the genus, or in different genera, if Macrobiotus were 

 subdivided on that character. 



I believe, however, that there has been much confusion over M. macronyx. Special 

 biological studies have been made by men little acquainted with species, on animals 

 supposed to be this species, and till quite recently few supposed that there were 

 numerous species of Tardigrada. M. macronyx was supposed to be the only fresh-water 

 species ; therefore any species found in water must, it was thought, be that species. 



M. macronyx, Duj. (7), is very insufficiently described. Dujardin's first descrip- 

 tion of the Tardigrade, published in 1838 (5), applies to an animal which he afterwards, 

 in 1851 (7), named M. lacustris. The earlier description is of little value, as it 

 undoubtedly confounds two or more species. He figures two sets of claws, totally 

 distinct, — fig. 6 (5) shows claws which, I think, may be taken as like those which he 

 (in 1851) ascribed to M. macronyx, — fig. 7 shows claws of the same type as M. ober- 

 hauseri, Doy. 



The description of M. macronyx given in 1851 (7), p. 163, is far from satisfactory. 

 The animal is 1 mm. long, and the long claws are -^ mm. long. The manducatory 

 apparatus (mouth, teeth, gullet, and pharnyx) is nearly \ of the total length. 



The pharynx forms half of the length of the manducatory apparatus. The 

 mandibles (teeth) are larger and more curved than in M. lacustris, and are not 

 bifurcate at the base. Of the eggs he says nothing. 



As to the teeth, not bifurcate at the base, I have seen no Macrobiotus without a 

 tooth furca, unless when in the simplex state ; and, moreover, Dujardin shows a furca 

 in his fig. 7. 



Leaving that character aside, the animal is characterised by the peculiar form of 



