3^4 E. H. STRICKLAND. 



while at the same time the larva has to depend to a large extent 

 on these threads for retaining any foothold on tin- rocks, for when 

 moving its position, the adhesive disc of the proleg frequently 

 loses its grip and the larva is \vashed clear of the rock. Very 

 rarely, however, the anchoring threads, which are always present, 

 break so that the larva is able slowly to draw itself once more to 

 its support. Sections of the Simulium larva disclose the fact that 

 there are very few other tissues in the body. The muscular 

 system is much reduced, and the only tissues available for attack 

 without rapidly killing the host are the fat-body and the sexual 

 organs, and I am under the impression that it is the latter which 

 are usually the original seat of attack. In frontal -sections of a 

 very young larva taken during March, only one testis could be 

 found, but on the other side of the body a small mass of minute 

 cells, taken at the time for small cenocytes, was situated a little 

 back of the normal position of the missing testis. The cells are 

 too small to show any structures but it is possible that this is a 

 diseased testis to which the spores made their way as soon as 

 they entered the body cavity. Later sections also show traces 

 of a very thin membrane investing the mass of "spores." 



I kept a large number of diseased larvae in running water, 

 hoping to see some of them pupate, but in every case they died, 

 and soon liberated the spores, whereas many of the healthy 

 larva 1 , which were approaching maturity, pupated in captivity. 

 It is thus evident that heavily parasitized larvae never pupate, but 

 die in the stream, liberating their countless spores in the water. 

 \Yhat happens to these spores I have been unable to ascertain. 

 Larvae were allowed to die in distilled water and the liberated 

 organisms were examined at intervals, but though they strongly 

 resisted decomposition they never showed signs of movement or 

 altered condition. Sections of pupse and adults obtained from 

 badly infested localities failed to reveal any cases of the disease 

 being carried beyond the larval stage. It is therefore probable 

 that the disease is not hereditary as is the case with pebrine, 

 and as before stated it was seen that the presence of this parasite, 

 in every case examined, apparently resulted in castration of t In- 

 best. It is, however, possible that among the vast numbers of 

 larva' a few were only slightly parasitized and did not have tlu-ir 



