PILAEIA SANGUINIS HOMINIS IN THE MObQUJTO. 375 



the margin of the body of the animal is broken at this point. Thus it would seem that 

 here there is a hole in the cuticle. When looked at directly from behind, or in front, 

 it appears round. From its first appearance, and until the last step of the metamor- 

 phosis is entered on, granular matter and minute nucleated cells are seen to escape 

 from this point. Very little pressure and sometimes even the mere immersion in water 

 is sufficient to bring about this granulo-cellular discharge from the anus. I do not 

 consider that this discharge comes from iuside an alimentary canal, but look upon it as 

 perianal tissue which the exterior tenuity of the walls of the rectum, and the absence 

 at this point of integument, permit to escape, rupture being favoured or brought about 

 by endosmosis of water used in mounting 



Coincident with the appearance of anus and cells the mouth advances in development. 

 From being pursed up it seems to open, and gradually four large fleshy lips are 

 fashioned (figs. 16 to 30). 



Then a line, at first very faint and broken, shows itself. Running in the axis of the 

 body for the most part, its destiny appears to be to connect mouth and anus. Around 

 this fine as it becomes thicker and longer, cells are seen to be arranged (figs. 14 to 25). 

 The line does not seem to extend in all cases quite to the anus, but terminates, as far as 

 one can make out, in advance of this some little distance among certain comparatively 

 large and prominent cells. By degrees this line, the rudiment of the alimentary canal, 

 becomes thicker, and the arrangement of nucleated cells around it forming the walls of 

 the alimentarv tube becomes verv distinct. In some instances the line itself is manifestlv 

 double-tubular. Probablv a fine membrane lines it. continuous at the mouth with the 

 skin, and is the lining-membrane of the future alimentary canal. 



How this alimentary line is produced it is difficult to say. It is certainly not a 

 process derived from the integument dipping in at mouth or anus ; for, in many 

 instances in which it is visible, it is only so about the centre of the animal, and is not 

 traceable into either mouth or anus. My impression is. that this line is produced 

 something after this fashion : — After the cells I have described as filling the bodv at the 

 beginning of the third stase have been formed, thev arrange themselves into two sets. 

 One set goes to the periphery of the body to form future muscular and fibrous walls ; 

 the other set accumulates in single file in the centre of the bodv in a line extending 

 from mouth to tail. The cells thus arranged in single tile divide and subdivide longi- 

 tudinallv as regards the axis of the Filaria, the lines of division radiating from the centre 

 of the original file of cells, like the segments of an orange. This would have the effect of 

 making the point of convergence of the Hues of cleavage very distinct — the alimentary 

 line. After a time the cells swell out or increase laterally, thus opening out their hue 

 of convergence, which thus is converted into a tube, the alimentary canal. This process 

 extends no further back than the anus ; but the central line of cells can sometimes be 

 traced as far back as the tail, and it is principally from having seen this post-anal line of 

 axial cells that I infer this method of explaining the formation of the alimentary line 

 and canal. 



■Wlide the alimentary line and canal are being formed, cells range themselves, as I 

 have just said, around the periphery of the Filaria, lining the skin. But between this 



SECOND SERIES. — ZOOLOGY, VOL. II. 55 



