"GROUSE DISEASE " STRONG YLOSIS 229 



denser portions of the food these metamorphosed forms now 

 rush about with great rapidity, and either wriggle into the 

 patches of open water or make their way on to the actual surface 

 of the culture, and may be seen standing out in numbers into 

 the moist atmosphere above, forming a kind of hoar frost on 

 the surface of the faeces apparently in search of oxygen. Those 

 larvae, which are fortunate enough to be near the edge of the 

 culture, ascend in the condensed water on the sides of the 

 Petri dish and make their way on to the upper part, eventually 

 reaching the blotting paper. Others will crawl out of the thin 

 edge of the culture medium and become stranded on the dry 

 glass. This metamorphosis takes place between the eighth 

 and sixteenth day from the commencement of the culture, 

 the difference in time depending almost entirely on the tempera- 

 ture at which the culture is kept. 



If the blotting paper be now removed, and the upper part The second 

 of the Petri dish be put aside, so that the moisture on its inner "encyst- 

 surface, which contains the actively wriggling metamorphosed ment - 

 larvae, be allowed to evaporate slowly, it will be noticed that 

 as the water disappears the movements of the larvae gradually 

 diminish and eventually entirely cease, so that ultimately the 

 larvae lie, sometimes making irregular figures like notes of 

 interrogation, sometimes coiled up like a watch spring (Fig. 33). 

 If drying proceeds sufficiently slowly, it would be found on 

 examining the dish with a hand lens that when all traces of 

 moisture have disappeared the little coiled larvae stand out as 

 turgid, glistening streaks. They seem to be capable in this 

 condition of retaining a certain amount of moisture within 

 their thick resistant cuticle for several days, and to make up for 

 any loss of fluid by evaporation by slowly retractihg the body 

 from either end and of detaching themselves from their cuticular 

 skin (Figs. 30, 31, 34). This retraction may go on to such an 

 extent that if one suddenly adds water once more to a Petri 

 dish containing such dried forms the little worms are found 

 enclosed in long sheaths that extend much beyond each end, 

 recalling the sheathed embryos of filaria seen occasionally in 



