SCOTTISH TARDIGRADA, COLLECTED BY THE LAKE SURVEY. 655 



may be called the echinogenitus type, has three nearly equal rods, the third slightly the 

 largest. The third type may be called the oberhduseri type. In this the process 

 attached to the gullet is very large, and there are only two other rods, which are 

 almost exactly equal, and usually short, often as broad as long. 



With each type there may be an addititional more obscure process of the end of 

 each row. This Richters aptly calls the " komma." It appears to be a reliable char- 

 acter, but there is some little doubt about this. 



Variability of the pharnyx. — The only variation noted is in the number of rods, 

 and appears to be a matter of age. The pharnyx is, I believe, very constant in adults, 

 but the young have sometimes one rod less in each row. In most species the well- 

 developed young in the egg have all the essential characters like the adult, but the 

 young of M. angusti and M. annulatus have one long rod in place of the two rods 

 nearest the gullet. These two rods are simply joined in the young, and become free in 

 the adult. In the hufelandi type of pharnyx they are usually permanently united. 



Structure of pharynx. — The true relation of the various parts of the pharynx and 

 their mode of working was first made intelligible by Albert Basse's beautiful sections, 

 figured in his instructive " Beitrage zur Kenntnis der Baues der Tardigraden " (22). 



The claws. — There are four well-marked types of claws. The hufelandi type has 

 the two claws of each pair united in their lower parts, say from one-third to two-thirds 

 of the length of the larger claw. A variety, of which M. coronifer is an example, has 

 a crescent-shaped ridge, sometimes bearing a series of spines, in front of each pair of 

 claws. The echinogenitus type has the claws of each pair united at the base only, or 

 for a short distance above it ; the pairs are similar, but one claw of each pair is some- 

 what longer. The macronyx type has the claws of each pair very unequal, the pairs 

 similar, the disparity less between those of the last legs. The oberhduseri type, 

 which might also be called the Diphascon type, as it prevails throughout that genus, 

 has one pair of claws slightly unequal, and joined at the base, the other pair consisting of 

 one short claw and one very long slender claw, apparently springing from the middle 

 of the back of the shorter claw, but movable upon it. 



There is usually no difficulty in assigning a species to one of these types, but 

 puzzling intermediate forms sometimes occur. The oberhduseri and echinogenitus types 

 are joined by a series of gradations. 



The supplementary points near the tips of the larger claws appear to be very 

 often two in number in the hufelandi type, and sometimes in the echinogenitus type. 



The eggs. — There are also four distinct types of eggs, but they fall into two great 

 groups — those which are normally laid in the cast skin of the animal itself, and those 

 which are laid free from the skin. The eggs laid in the skin, which may be called the 

 macronyx type, are always smooth, usually oval or elliptical, but sometimes nearly 

 round. There are three varieties of eggs laid free, — first, the hufelandi type, which is 

 round, with the surface covered with processes, generally uniform and evenly spaced 

 over the surface (the egg may be oval [coronifer], and the processes may be irregular 



