TARDIGRADA 93 



features identical, the idea of the value of the characters grows. This happens most 

 frequently in colonies got at one place and time. Now a whole brood, or even a 

 whole colony, may possess some little peculiarity which would not be permanent in a 

 race of animals having the sexes distinct, and where cross-fertilisation may occur. 

 The case of the Bdelloid liotifera, which will be discussed in a subsequent paper, is 

 very different, as only females are known. The reproduction being parthenogenetic 

 there seems to be no check to the multiplication f slightly marked species, and the 

 study of certain groups of forms bears this out. 



The group of Tardigrada has hitherto been fortunate in that it has not attracted 

 the attention of any too-enthusiastic discoverer of species. Professor Richters has 

 shown a commendable reserve in simply describing and figuring those doubtful 

 Echinisci, without giving them names. 



This appeal's to be the right course to take, in the present state of our knowledge, 

 and yet these unnamed forms are a trouble to the student. There is nothing to get 

 hold of, and the memory recognises them not even reference to them is laborious. 

 Since species are a human convenience one is sometimes tempted to wonder whether 

 the convenience of naturalists is better served by describing unnamed forms than by 

 lightly naming them in the good old way, with, however, its accompaniment of 

 burdening the synonymy when we come to know better. 



In the genus Macrobiotus the species difficulty takes another form. There is little 

 external variability. As few of the species have superficial processes there is little 

 difficulty of the sort we have in Echiniscus. 



Variability is seen in the coloration the animal may be colourless when young, 

 and highly pigmented when old ; in the claws the amount of union of the pairs 

 may vary considerably ; in the rods of the pharynx the first rod, next the gullet, 

 may be a long one, or divided into two shorter ones, and the " comma " may be 

 present or absent ; in the eyes, which may be present or absent. Some of these 

 differences are known to be dependent upon age. The limits and value of others are 

 not definitely known. 



Two forms of Macrobiotus may differ in two of the most important characters used 

 in discriminating species (claws and pharynx for example), yet the range of variation 

 of each of these characters, taken separately, is wide enough to embrace both forms. 

 Whether it is likely that two or more characters would vary simultaneously, to the 

 extreme extent, in animals which are of the same species, we cannot tell. If it were 

 so specific distinctions in the genus would to a large extent break down, and we would 

 have only a few species, representing the principal types of claws recognised 

 (hufolandi, oberhiiusem, dispar), or of eggs (the hufelandi type, the hastatus type, 

 and the smooth eggs). 



Another difficulty with Macrobiotus is that series of species agree so closely in all 

 the characters of the adult that they cannot be distinguished with certainty, and it is 

 necessary to find the egg before a species can be identified. These series of closely 



