6 MB. D. J. SCOTJKFIELD ON ENTOMOSTEACA 



with the subject in hand, but only the two last seem to demand 

 special consideration. 



A cursory examination will show that the dark colour alluded 

 to is not distributed uniformly over the whole body, but that 

 it occurs in definite patches. Viewed from the side (PL I. 

 fig. 1) there appears a small patch on the ventral face of the 

 head between the eye and the rostrum, another patch covering 

 the ventral third, of the valves, which, although not quite reaching 

 the posterior margin, extends into the shell-spines, and a fainter 

 patch along the dorsal line of the body. The small antennae and 

 the ventral surfaces of all the joints of the large antennge, together 

 with the pre-anal portion of the post-abdomen, are also evidently 

 darkened. The front or vental view (PI. I. fig. 2) shows all 

 the above mentioned areas, necessarily with the exception of the 

 dorsal one ; and besides revealing the fact that the labrum is 

 also considerably blackened, it proves that the ventral patches 

 of colour are even larger than appeared from the side. A curious 

 little fact may be pointed out in passing, in relation to the patch 

 on the head, namely, that the colour is absent just over the small 

 eye-spot. This seems to show that the latter is really a func- 

 tional visual organ. The colour in all cases is produced in part 

 by a staining of the chitin, proved by the fact that the moulted 

 shell and appendages retain the characteristic dark areas, and in 

 part by a number of ovoid pigment granules contained in the 

 cells immediately underlying the chitinous integument. These 

 granules are distributed, it is true, all over the surface of the 

 body, but only sparingly in the uncoloured portions, while 

 under the darkened areas they are very abundant. Their colour 

 is not quite black, but rather a dark brown ; and this is also the 

 case with the darkened portions of the carapace and appendages. 

 The physiological cause of these peculiar colour-markings is, so 

 far as I am aware, quite unknown. Their probable utility will 

 be seen, however, when the habits of the animal are considered 

 in a later part of this paper. 



Passing now to an examination of the setse fringing the ventral 

 margins of the valve?, it will be found that, when looked at from 

 the side (PI. I. fig. 3), the anterior and posterior members of 

 the series are both longer and coarser than those in the middle. 

 The anterior ones can also be seen to have a small branch directed 

 forward. But beyond this, and the fact that with dark-ground 

 illumination there is an appearance which suggests that an 



