10 MR. D. J. SCOTIEriELD ON ENTOMOSTEACA 



readily made out to be capillary depressions. They must, how- 

 ever, be either depressions or elevations ; and since it is impos- 

 sible to imagine how the latter could sustain a weight, the 

 conclusion is inevitable that the irregularities seen are actually 

 depressions. But how can capillary depressions be formed by 

 such a small body coming from beneath the surface ? So far as 

 I am aware, there is only one way in which a capillary depression 

 can be formed under these conditions, and that is by the piercing 

 of the surface-film by a more or less water-repellent substance. 

 By making the assumptions, therefore, that the minute chitinous 

 ventral setse and scales are water-repellent, and that they can be 

 forced through the surface-film by the muscular power of the 

 animal, neither of which can be considered a very large assumption, 

 it is manifest that a tolerably clear general notion may be formed 

 of the means by which ScapTioleberis makes use of the surface-film. 

 The water-repellent scales and setse, pushed through the film, 

 give rise to a number of capillary depressions (apparently four, 

 produced, I believe, by the anterior and posterior groups of 

 ventral setae) which are large enough to support the animal, but 

 not too large to prevent it from breaking contact with the sur- 

 face and retreating below when required. While the principles 

 involved are thus essentially the same as in the case of the 

 helplessly floating forms already referred to, in this instance 

 tliey are turned to good account by means of special organs of 

 limited extent, the whole arrangement being under the control 

 of the animal. 



Coming now to Notodromas monacha (PL I. figs. 6 and 7) it 

 will be noticed that, from the present point of view, its chief 

 characteristics are the dark coloration of parts of the shell- 

 valves, and their flattened ventral surfaces. These, it will be 

 seen, are precisely analogous characters to those specially noted 

 in ScapJioleieris. 



The colour, although not so arranged as in the Cladoceran, is 

 nevertheless distributed in patches in a very definite manner. 

 On each valve there is a practically continuous band of varying 

 intensity stretching diagonally from the upper part of the 

 anterior margin to near the posterior end of the ventral margin, 

 from whence it turns forward and forms a band along the greater 

 part of the edge of the valve, covering very nearly the whole of 

 the flattened area. Two little isolated patches of colour also 

 usually occur between the principal diagonal band and the pos- 



