374 DE. P. MANSON ON THE METAMOEPHOSIS OF 



being differentiated from the rest of the animal simply by its not having partaken in the 

 general swelling (figs. 4-10-38, 41, and 42). 



At this stage movement still persists ; but as the body swells, motion becomes fainter 

 and more intermitting, till, in many examples, it finally ceases soon after migration has 

 been effected. There is a tendency now for the oral end to become tapered, and more 

 conical, one or more black points being visible at the very end. 



The bodv continues to swell till it has more than trebled its original diameter, and 

 become shorter by one third. Thus the tail comes to look a mere appendage stuck on 

 one end of a sausage-shaped mass. 



At first, and often all through the subsequent steps of the metamorphosis, the tail 

 does not correspond with the axial Hue of the body but is quite to one side. In others, 

 especially at a later stage, the position of the tail appears to be, and possibly is, axial, 

 although this effect is produced in many instances by the position the animal is viewed 

 in, according as the tail is to right or left, above or below ; in both the latter positions it 

 must appear axial, although it may really be quite to one side. 



When the body has attained a thickness of about the fifteen hundredth or the two 

 thousandth of an inch it lies sometimes outstretched, sometimes gently bent, occasionally 

 curved on itself, so that mouth and tail are almost touching (fig. 42). The oral end 

 gives the impression that there is an orifice there, but that it is firmly pursed up. 

 Movement of the body is now rarely seen. Occasionally in some there is a slow general 

 bending and extension, and in others a peculiar shivering movement. The tail still at 

 times is vigorously flexed and extended. ]S T o organ or structure of any definite kind can 

 be made out even with a high power ; only a little in advance of the tail, where the anus 

 is afterwards formed, sometimes an aggregation of minute cells with relatively large 

 nuclei can be seen (fig. 4). The rest of the body is made up of a cloudy granular 

 material enclosed in a very delicate integument. The latter can be made out only after 

 crushing of the body and partial escape of contents, or when the slide has partially dried. 

 In such circumstances we may sometimes see a funnel-shaped mouth into which the 

 delicate integument is reflected (fig. 10). 



The thickening of the body, differentiation of the tail, and first indications of a 

 distinct mouth constitute the second stage of the metamorphosis, and usually require 

 two or three days for their completion. 



About the third or fourth day we often find the body of the sausage-shaped Filaria, 

 which hitherto has shown little or no structure, filled Avith a crowd of minute shiniug 

 granules (fig. 11). These, I believe, are nuclei which from extreme transparency and 

 refracting properties, similar to that of the stroma of the animal's body, could not at au 

 earlier stage of development be recognized. In others again, apparently somewhat 

 more advanced, cells to which these nuclei belong become obscurely visible (figs. 12 to 

 20). These cells are exceediugly minute. Each possesses a distinct nucleus, aud 

 together they make up the entire mass of the body and tail inside the delicate cuticle. 



About the time the cells become visible the rudiment of the future anus shows itself 

 as a sort of pit or vacuole a short distance in front of the tail (figs. 12, 13, 15, 39, etc.). 

 When viewed in profile this pit or vacuole seems infundibuliform, and the outline of 



