212 F. W. EDWARDS. 



Before passing to tabulate the species and consider them individually there are a 

 few points which seem to be of sufficient general interest to claim attention here. 



Method of Rearing and of Association of Larvae and Fwpae with Adults.-lt was pointed 

 out by Newstead* that the pupae of Simulium when removed from the water and 

 placed in a moderately damp atmosphere without superfluous moisture will readily 

 complete their transformation into adults. This method of rearing has proved 

 invaluable, and provided the vessel in which the pupae are kept is not too small, and 

 is kept slightly moist, it practically never fails : thousands of specimens have been 

 reared in this way. If however a male pupa which it is desired to rear should die, 

 it can easily be identified by dissecting out the genitalia. 



In a colony of larvae where even a moderate proportion are full-grown, some are 

 sure to be found which exhibit a round black spot on each side of the prothorax, 

 conspicuous even to the naked eye. This is the respiratory organ of the developing 

 pupa showing through the larval skin, its component filaments bein.g coiled up into 

 a small space. The filaments can be very easily dissected out with a pair of needles, 

 and a positive identification of larva and pupa obtained. If in the same colony 

 there are also blackish, well-developed pupae, the species can be identified by dis- 

 secting these without the necessity of waiting for specimens to hatch out. It is very 

 desirable to identify larvae by this reliable method, since one very frequently finds 

 several species living together in the same colony; though in a small area of a few 

 square inches one will usually greatly outnumber the others. 



Over-tvintering. — Some species, notably S. ornatum, appear to continue breeding 

 throughout the winter, even in the coldest weather, though, as might be expected, 

 the rate of development is greatly retarded. Of such species there must be at least 

 three broods in the year. Others, such as S. latipes, pass the writer as young larvae, 

 developing rapidly in the early spring ; probably these are normally single-brooded. 

 The species which appear in such vast numbers in spring in our muddy-bottomed 

 rivers may possibly winter in the mud in the egg stage, bub I have not been able to 

 obtain any positive evidence of this. Another possibility, and perhaps a more likely 

 one, is that the females may hibernate, but I have never found them in a torpid 

 state. However, as Mr. Hamm has pointed out to me, the specimens of S. equinum 

 and S. argyreatum captured very early in the year are generally, if not always 

 females. More observations are needed on this point. 



Oviposition. — ^\^ery little is yet known as to the egg-laying habits of the different 

 species, but it would seem that great variation exists. I have been able to confirm 

 the very interesting observations of Mr. H. BritteiDl on S. equinum, and have added 

 some further particulars below. I have also found and hatched the eggs of S. aureum, 

 which, unhke those of S. equinum, are hard-shelled and not enclosed in a mass of jelly; 

 the newly-hatched larva of this species also has a much more strongly-developed 

 egg-burster, so that it would seem that this species may be adapted to resist 

 desiccation in the egg state. 



Habitat of Larvae. — ^The larvae which I have met with may be classified according 

 to their habitat into (1) those which live on water-plants (or other objects if available) 



* Ann. Trop. Med., i, p. 40. 



tEnt. Mo. Mag. (3), i, 1915, p. 150. 



