26 THE VICTORIAN NATURALIST. 



been witnessed that the full explanation of the arrangement 

 was definitely understood. In the living cercaria the cells are 

 confined to two ducts, which end blindly behind but open in 

 front just behind the anterior sucker. The cells are probably 

 cystogenous in function, yet only a few seem to be used up in the 

 actual process of making the cyst. Shining through the cyst a 

 circlet of spines is clearly visible, encircling the anterior sucker, 

 and if the cyst is ruptured this circlet is seen to be made up of 

 a double row of small spines. The ring is broken by the 

 anterior sucker, and at the points lying near its posterior border 

 are two patches, each bearing four large pointed spines. Exceed- 

 ingly minute spines cover the anterior end of the embryo, and 

 extend down the body to the level of the posterior border of the 

 ventral sucker. Rudimentary spines can be made out on some 

 of the active cercarine, but growth of the spines seems to proceed 

 most rapidly in the period immediately following encystation. 

 This example affords evidence of what is known as an " armed " 

 variety of embryo fluke — the armour referring to the presence of 

 specially modified spines or stylets, which are, doubtless, of use 

 to the embryo for attachment purposes in a final host. The 

 cysts themselves occur not only in the liver, but also in the 

 albumen gland and near to the pericardium, and in one instance 

 a redia also contained cysts. 



Another interesting cyst occurs in the snails Isidora lexturata 

 and Limnea le.ssoni. It is just twice as large as most of the 

 others, being about J 3 in. in size ; so large, in fact, that no active 

 cercaria has been seen which can be exactly fitted to it, and it is 

 probable that the earlier stages have yet to be observed. The 

 semi-transparent cells which have already been described in 

 connection with the other cyst here take the form of a crescent, 

 the edges of which give off branching processes. In the space 

 between the limbs of the crescent structures like the teeth of a 

 comb can be seen (fig. 2). If now the cyst be ruptured carefully, 

 this comb-like structure assumes the shape of a nearly complete 

 ring in the region of the anterior sucker — the ring being made 

 up of about thirty-seven large spines. On either side of the 

 pharynx is a tuft of four spines, then the others follow in a single 

 row till they meet in the mid-dorsal line. Covering the whole of 

 the anterior portion are small spines which extend, as in the case 

 of the fluke before described, as far as the ventral sucker. At 

 this stage the embryo has practically all the rudimentary struc- 

 tures of an adult fluke. 



Occurring side by side with the cysts already described, a 

 great number of somewhat smaller cysts, about ^bo in - m 

 diameter, were occasionally met with. No opaque cells were 

 present, but the included protoplasm presented a uniform 

 granulated appearance. In most cases the cysts occurred in 



