90 J. MURRAY 



Many species of Macrobiotus cannot be distinguished with certainty unless the 

 egg is seen. The mere presence of eggs beside the adults is of no use, although there 

 may be a presumptive relationship in such cases. The relation must be demonstrated, 

 and this can be done in two ways : first, by finding in an egg the young so far 

 advanced that the claws and pharynx can be recognised ; second, by finding, in the 

 adult, eggs so far advanced as to show the characteristic processes. The first way is 

 the more generally useful. The second may be of greater use than the beginner 

 would suspect. The eggs are soft till they are almost ready for laying, and the 

 processes, when formed, are still so soft that they are squeezed flat against the shell 

 by the enclosing membrane. If the membrane can be torn, and the eggs released, the 

 processes often stand up and can be recognised. 



All species of Macrobiotus, and probably other water-bears, may be found in what 

 is called the " simplex " state. They are then devoid of teeth, of rods in the pharynx, 

 sometimes of all the mouth parts. Plate founded the genus Doyeria on an animal in 

 this condition. The simplex state is now explained as a part of the moult, though 

 it does not occur simultaneously with the casting of the skin. Identification of an 

 animal in the simplex condition is difficult, as one of the most important characters 

 is lacking. 



Many water-bears, perhaps all, encyst themselves. This appears to be a sort of 

 hibernation, in which a quiescent period is passed in a special protective case. Some 

 species, when encysted, undergo a simplification going far beyond the ordinary 

 " simplex," for they lose all recognisable organs, teeth, pharynx, and claws, and 

 afterwards acquire them anew. 



Diphascon. The genus differs from Macrobiotus solely in having the gullet 

 elongated between the teeth and the pharynx. As specimens of Macrobiotus are 

 sometimes found which have the gullet elongated, the value of the genus is very 

 slight. Nevertheless, I believe Diphascon to be a natural group. All the species 

 have claws of one type, known as the Dipliascon type, which is also found, but rarely, 

 in Macrobiotus. Many of the species have the pharynx very narrow, but others 

 have it quite round. Most of the known species have no eye-spots. 



In distinguishing species the chief points to attend to are the diameter of the 

 gullet, which varies extremely, the proportions of the pharynx, and the number and 

 sizes of the rods or nuts in it. 



In outward form there is little variety. All are very similar except D. bnllatum, 

 which is short, nodose, and papillose, and D. augustatum, which has a heavy body, 

 but tapers to a very narrow head. 



As a rule the animals of the genus are small, but some very large forms inhabit 

 the arctic regions. 



The eggs are smooth, and are laid in the cast skin, as in Echiniscus and a large 

 section of Macrobiotus, 



