86 MR. F. BALFOUR-BROWNE ON THE LIFE-HISTORY 



various water-beetles both Hydradephaga and Hydropliilidse ; and 

 as a rule they do very well, but occasionally an egg shows signs 

 of being xmhealthy, that is, the surface becomes the home of 

 numljers of minute Protozoa and Algae. Such an egg if left to 

 itself invariably dies, but I discovered a way of treating it which 

 usually saved it, and this was by saturating the cotton-wool with 

 a solution of methylene blue. Any moderate strength seemed to 

 be suitable, and the methylene blue killed off the Protozoa or Aigse 

 without injuring the egg. But the efiect of the methylene blue 

 was not confined to destroj'ing the Protozoa and Alga) on the 

 egg-shell. It did not in a,ny way injuriously affect the develof)ing 

 embryo, but certain parts of the living tissues took up the stain 

 and stood out bright blue. The staining varied with different 

 individuals, with the same individual at different times and 

 possibly also with different strengths of methylene blue, but in all 

 cases the embryonic appendages of the first abdominal segment, 

 which are well developed in this species just as they are in 

 Dyiiscus lappcnicits, took up the stain {v. PI. I. figs. 9, 10, & 11). 



Otherwise the staining was very irregular. In the case of one 

 larva just ready to hatch, the dorsal phar3'ngeal muscles and the • 

 malpighian tubules were stained, and on the left side of each 

 thoracic segment and of the first two abdominal segments a short 

 line, curved in the thoracic, straight in the abdominal segments, 

 was also stained. At one end this line came to the surface of the 

 embryo and suggested a spiracle, although there is no pro-thoiacic 

 spiracle in the larva and the spots were above the real meso- and 

 meta-thoracic spiracles which were also stained. Incidentally it 

 may be mentioned here that none of the spiracles are functional 

 in the larva. In the abdomen of this specimen parts of the 

 dorsal longitudinal muscle system under the terga were stained, 

 but not evenly, certain strands having taken the stain, others 

 not having taken it. In the alimentary canal was some greenish 

 fluid which I took to be methylene blue changed by the action of 

 the secretions. 



I give this example merely to show the strange effect of 

 methylene blue, and without making any attempt to explain it, 

 I assume that the parts which stain are in some wa}^ active at the 

 time they stain. For instance, possibly the one-sided staining 

 of the dorsal longitudinal muscle system in the specimen referred 

 to may have indicated that those muscle-strands were doing work 

 while the corresponding strands upon the other side were doing 

 none. If this suggestion is sound it might perhaps be possible, 

 by watching any embryo develop in an egg kept in methylene 

 blue, to recognize various parts functioning at different times. 



The staining of the first abdominal appendages, which disappear 

 after hatching, is also of some interest if this suggestion is correct. 

 These appendages first appear when the embryo is about three 

 days old and after the three pairs of thoracic appendages, but 

 they are more distinct than any of the following abdominal 

 appendages which rapidly disappear, and they persist, as more 



