322 E. H. STRICKLAND. 



to occur in the same individual, another form of cell (Plate Y., 

 Fig. 1 8) was found in much smaller numbers, but possibly in some 

 way connected with them, for it was seen in association with 

 each form, but was not found in healthy larva?. This cell, which 

 varied much in diameter from but little more than the numerous 

 "spores" to three or four times the length of their longest axis, 

 was apparently globular in form, and in a fresh state was very 

 transparent and could only be discerned with difficulty. The 

 following characters, however, were seen. The substance of the 

 cell was finely granular, and often contained a number of large 

 transparent globules. When fixed and stained the only dif- 

 ferentiation was that of a large dark mass, apparently the nucleus 

 (Plate V., Figs. 18, a and b). In some cases these cells seemed to 

 be dividing (Plate V., Fig. 18, c}. 



In the face of all these diverse types of cell, which live in 

 precisely the same way, it is evident that the forms first found 

 are not spermatozoa, and further the fact that the flagellum is 

 replaced in one "species" by a flattened disc eliminates the 

 possibility of their being Flagellates. It is therefore probable that 

 one must look to the Microsporidia among the Sporozoa as the 

 group to which these bodies belong. It is further noticed that 

 many of the forms are very similar to those met with in the 

 genus Ghigea to which the well known pebrine disease (G. bomby- 

 cis) of silk-worms belongs. One must therefore conclude that 

 it is a pebrine-like disease, which is killing off a high percentage 

 of the Simuliid larvie in the neighborhood of Boston, though on 

 account of the vast difference in structure and mode of life of 

 the two hosts the life history of the parasite in the SimuUum 

 larva 1 is very unlike that described by Pasteur ('70) and Stempell 

 ('09) in their work on the disease in silk-worms. 



LIFE HISTORY OF THE PARASITE IN ITS HOST. 

 As in the case of Mermis, I know very little about this, since 

 I did not discover ii (ill the final stages of the larva were being 

 approached, and in every instance but one ii was apparently in 

 exactly the same condition, namely, the "spores" were all 

 formed and were simply awaiting the death of their host and its 

 resulting decomposition to escape into the water. 



