TARDIGRADA 89 



oberhciuseri and a few other Macrobioti) has the two pairs dissimilar. One pair has 

 two claws, of which one is longer, united at the base ; the other pair has one very 

 long claw (bristle-like in M. oberhanaeri), which is loosely attached to the middle of 

 the back of a smaller claw. 



The echinogenitus type has two similar pairs of claws which are united at the base 

 only. The claws of each pair are equal or unequal. This type is not so distinct from 

 the hufelandi type as it seems, and is connected with it by a series of forms 

 having the claws united more or less above the base.* The typical form has the 

 claws very widely divergent. Forms having the pairs unequal lead to the 

 Diphascon type. 



The skin varies in texture, &c. It may be smooth and hyaline, papillose, or 

 more or less pigmented. Often the young are transparent and colourless, and the older 

 ones increasingly pigmented. The pigment is rarely of specific value, as most of the 

 large old animals become brown, but in M. oberhciuseri it is characteristic. A few'species 

 are papillose (M. annulatus, M. nodosus, &c.), and a few bear processes on the skin 

 (M. ornatus, M. tuberculatus, M. sattleri, M. papillifer, and sometimes M. dispar). 



The eyes are of doubtful specific value. They are usually dark brown or black, 

 occasionally red. Though it is believed that the presence or absence of eye-spots is 

 characteristic of each species, there is enough variation to make the character 

 unreliable. It should, however, always be noted in descriptions. 



The fat-cells are generally of no specific importance. In a few species (M. 

 coronifer, M. islandicus, M. rubens, M. occidentalis, &c.) they have a characteristic 

 colour, red, yellow, orange, or brown. 



The egg varies greatly. It is either smooth or covered with processes which are 

 characteristic for each species. The smooth eggs are never quite spherical, but 

 shortly oval, rarely narrowly oval. They are left in the skin at the moult. The 

 ornamented eggs are spherical, with a very few exceptions (M. coronifer, M. pullari, 

 &c.). The form of the processes should be noted, the distance (if any) separating 

 them, and the nature of the egg-shell where free from processes. In a number of 

 forms the shell is areolate. It is thick, and composed of two layers, the space 

 between which is divided into a number of equal chambers, showing on the surface 

 as hexagons. From some of these the processes spring, at equal distances apart. 

 The turgidity of the processes destroys the regularity of the hexagons, and additional 

 septa in the chambers give rise to a variety of patterns in the " areolation." 



The spiny eggs are laid free, not enclosed in the cast skin. An intermediate type 

 of egg has the shell ornamented with rods, which are embedded in a hyaline substance, 

 so that the surface is even (M. arcticus, &c.). In M. hastatus these rods have tops 

 shaped like fleurs-de-lis, which project above the general surface. 



* Prof. Richters informs me, in a recent letter, that he has ascertained that M. echinogenitus and related 

 species have the claws separate, but close together, in embryos in the egg, and that they join afterwards. 

 The adult M. echinogenitus has claws of the hufelandi type, not V-shaped. 



BRIT. ANTARCT. BXPED. 1907-9. VOL. I. N 



