1GG MR W. E. HOYLE ON" 



The Enclosing Cyst. 



The parasites, to the number of about ten, were enclosed in cysts in the 

 mesentery, and their appearance is shown in the accompanying 

 woodcut (fig. 1). Each is coiled into a more or less complete 

 circle, and, in every case examined except one, the ventral sur- 

 face formed the convexity of the curve. 

 Fig. 1. General appear- The cyst itself presents nothing in its structure worthy of 

 parasite. * eucy5te special note ; it consists of closely interwoven fibrils of connec- 

 tive tissue, imbedded in a quite homogeneous matrix ; the wall is about O^Oo 

 mm. thick, and it is more compact towards the inner than the outer surface. 



The External Appearance. 



The form of the body is (PI. XXVII. fig. 1), speaking generally, cylindrical 

 in the anterior half, and slightly tapering in the posterior, until it ends in a 

 blunt cone. In some specimens the last two segments presented an appear- 

 ance which may be aptly described in the words used by Diesing in speaking of 

 another species, "cute externa in form& prseputii"; but this was by no means 

 constant. 



The head is hemispheroidal, and is followed by a smooth cylindrical portion, 

 which is of very variable length ; in some cases it scarcely seems 

 to exist at all, whilst in others it measures from 2 to 3*5 mm. (cf. 

 PI. XXVII. fig. 1, and woodcut, fig. 2). 



This is succeeded by a number of annuli, which give the 

 'face of thehead! 1 body a decidedly vermiform appearance, although, as will be 

 seen in the sequel, this segmentation is scarcely at all reproduced in the internal 

 organisation. 



The number of the annuli varies with the sex, and also, though to a less 

 extent, with the individual ; it amounts in the males to 16 or 17, in the females 

 to from 18 to 22. Each of these rings is separated by a constricted portion of 

 the body, which may conveniently be termed the " interannular space"; these 

 are somewhat less than the annuli, not only when measured transversely to the 

 creature, but also longitudinally, except when it is very fully extended, under 

 which circumstances the two sets of rings become about equal. Furthermore, 

 the interannular spaces are of much weaker consistency than the annuli, as will 

 be explained in treating of the internal anatomy; and in correlation with this fact, 

 it is to be noticed that when the animal is coiled up, it is the interannular spaces 

 which give way to allow of this, the annuli scarcely undergoing any change at 

 all in breadth, but approaching each other on the concave aspect of the curve. 

 On the ventral surface of the head, and about 1 mm. from its anterior 



