E. H. STRICKLAND. . 



The length of the larvae next claims attention. No larva con- 

 taining this parasite was found to be exceptionally large ; whereas, 

 as before mentioned, many were extremely small, measuring some 

 2 -75 or 3-5 mm - at a time when all normal larvae measured some 

 9 mm. or more. This may possibly require a similar, though 

 opposite, explanation to that suggested on page 281 to account 

 for the large size of the individuals affected by the Mermis. 



In confinement these small specimens were extremely restless, 

 they were continually twisting about and moving over the sides 

 and bottom of the jar with a peculiar jerky movement. The 

 larger, and more heavily parasitized, larvae on the other hand 

 were more sluggish though nol more so than the healthy larvae. 



The effect of these parasites on the histoblasts is very hard to 

 state with any certainty. Fig. 13 is an illustration, made with 

 a camera lucida, of the histoblasts of a nearly mature individual. 

 In this case the parasite was confined to the abdomen. It will 

 be seen that the discs are but half developed (compare with Fig. 

 6). In other cases, however, the development of the discs was 

 not, so far as could be seen, affected in any way till pigmentation 

 of the respiratory filaments commenced. Then it was noticed that 

 the entire histoblast only turned a slate gray color instead of 

 blackening at tin- apex of the filaments and finally over the 

 complete disc. In other cases, however, the discs entirely 

 blackened in a perfectly normal manner. 



\Yhen colonies of parasites are located in the thorax, as is not 

 infrequently the case, the histoblasts are materially decreased 

 in size, while in the very small specimens development appeared 

 to have been arrested. This is hardly surprising. My general 

 conclusions were that the parasite affected the histoblasts but 

 little, though the larvae rarely advanced so far toward maturity 

 that the respiratory filaments became pigmented. It should be 

 noted that the power of spinning silk was in no way affected by 

 the presence of this parasite. 



NATURE OF THE PARASITE. 



While visiting other localities I made numerous observations 

 on the larvae to be found in the streams, and was much surprised 

 to find that species of the parasite were extremely common and 



