ANTARCTIC TARDIGRADA 97 



As M. arcticus was originally described from an egg containing the young ready 

 to hatch, and the adult had never been seen, it is here redescribed from adult 

 examples. The principal differences are that the rods in the pharynx are longer in 

 the adult (they are nearly round or quadrate in the young), and that it acquires a 

 brown pigment like that of M. hnjelandii. 



Detailed description. Length 500 /u. and upwards. The young is perfectly 

 hyaline, and has the long claws as slender and bristle-like as those of M. oberhciuseri. 

 The long claws become a little thicker in the adult. They are strongly curved 

 towards the tip, which is not the case with oberhauseri, 



The gullet is narrow, and is expanded at the end in the pharynx into a prominent 

 thickened flange. In the adult the rod nearest the gullet is between three and four 

 times as long as broad the second rod is a little shorter, three times as long as 

 broad, or rather less than that. 



The stomach is voluminous : about a dozen of its component cells are visible in 

 dorsal view. They are filled with large granules of a brownish colour, and there are 

 deeper brown patches. About the middle of August many were observed which had 

 the stomach green or deep blue. Macrobiotus with blue stomach has been noticed 

 in Scottish lochs and in the Arctic. 



Four unripe eggs have been seen in the body at once. The eggs are spherical or 

 very shortly oval, 96 p. in diameter. The thickness of the shell is about 5 or 6 n, but 

 varies considerably. The eggs often appear to be viscous, and have much adherent 

 material : some are quite clean and don't seem viscous. It may be that they are 

 viscous when first laid, and become hard afterwards. 



Habitat. In nearly all the lakes about Cape Royds and Cape Barne, extremely 

 abundant. 



It was the first water-bear which we found. On March 15 we obtained it, and 

 also eggs, among dried vegetation on the ground. This had doubtless originated in 

 a lake. It was most abundant in Coast Lake, where we could always get great 

 quantities. 



In Blue Lake on July 17 it was found alive at the bottom, on a thin pellicle of 

 vegetation under 1 5 feet of ice. 



In the experiments made to test the vitality of rotifers, many water-bears of this 

 species were present with the rotifers. They endured equally well exposure to the 

 greatest Antarctic cold, and repeated freezing and thawing, at weekly intervals, for 

 months. They were not subjected to heat. 



After being kept dry for a year, and conveyed on a voyage through the Tropics ' 

 to England, no adult animals revived, but the eggs retained their vitality and some jx<* 

 hatched out, and were exhibited at the Quekett Microscopical Club by Mr. > 

 Scourfield. 



M. arcticus appeared to be a thorough pond-dweller, and was never found among 

 mosses at Cape Royds. Nevertheless, in mosses which Priestley brought from the 



BEIT. ANTARCT. EXPED. 1907-9. VOL I O 



