212 J. MURRAY ON PHILODINA MACROSTYLA, EHR., 



Among the many forms of P. aculeata, there is only one which 

 I consider to be a stable variety. The variety crystallina has 

 a very distinct surface texture, which appears to be constant, 

 and no intermediate forms between it and the type have been 

 seen. It is quite as distinct from the three species as they 

 are from one another, but as it has also the dorsal spines 

 precisely agreeing with the commonest Scottish form of 

 P. aculeata, I prefer in the meantime to subordinate it to 

 that species. 



Form and Structure. 



The three species of the macrostyla group are so exactly 

 alike in their general organisation, that, if we suppose the two 

 spiny species deprived of their spines, there would remain no 

 other difference between them, except the lack of eye-spots 

 in P. spi?iosa, a character known to be variable in P. macrostyla. 



A general description of the outward form and internal 

 structure, as far as we need consider it, will fit all three equally 

 well, and the specific differences can afterwards be given in 

 a few words. 



It is not intended to enter minutely into structures which 

 are common to all Bdelloids, but simply to describe with sufficient 

 detail the form and proportions of all parts by which the 

 macrostyla group is marked off from the rest of the genus. 



I have not been able to make any minute study of the 

 organisation and physiology of these animals, valuable though 

 such study would be, had one time for it. Though they are not 

 by any means typical Philodinae, they are typical Bdelloids, and 

 there is no reason to think that exhaustive study would show 

 any important departure from the central Bdelloid type. I have 

 made no experiments and traced no life-histories, but simply 

 observed the animals carefully, as far as opportunity and the 

 instruments at my command permitted, and noted all points 

 of form and structure, whether of generic, specific, or merely 

 varietal value, wherein they differ from other Bdelloids and 

 from one another. 



Form. — Creeping or feeding the animals have the ordinary 



