TBEMATODA 49 



and round on its own axis, and also describing gyrations and 

 circles of different degrees of range in the water, the latter 

 movements being accomplished by bending the body upon itself 

 to a greater or lesser curvature. The embryos of Bilharzia and 

 other infusoria exhibit the same behaviour, and, as Leuckart 

 observes, when these embryos knock against any obstruction, 

 they pause after the blow, as if to consider the nature of the 

 substance they have touched. As in the case of fluke embryos 

 generally, the ciliated covering eventually falls off and the 

 embryo reassumes a more or less oval figure, at the same time 

 changing its swimming mode of progression for the less digni- 

 fied method of creeping. In the free ciliated condition the 

 embryo of the common liver-fluke measures, according to 

 Leuckart, ~" in length, the anterior broad end being ~". The 

 cilia have a longitudinal measurement of -o^" . 



According to the observations of Dr Willemoes-Suhm, the 

 cilia of the embryos of the Distoma megastoma are limited to 

 the anterior pole of the body. This is also the arrangement, as 

 Leuckart first pointed out, in Distoma lanceolatum (fig. 18). 

 On the other hand, Pagenstecher has shown that the embryos 

 of Distoma cygnoides and Amphistoma (Diplodiscus) subdavatum 

 are ciliated all over, an observation which, as regards the latter 

 species, has been confirmed by Wagener and others. Dr 

 Pagens teener's original statement to the effect that " intracho- 

 rional germs of trematodes offer no distinctive characters/' 

 must, therefore, in the present state of our knowledge, be 

 accepted as a general conclusion admitting of many exceptions. 

 In the early stages of development the embryo of Distoma 

 lanceolatum occupies the centre of the egg, and according to 

 Leuckart has its conical head invariably directed towards the 

 upper pole of the shell, or, in other words, to that end of the 

 egg which is furnished with a lid-like operculum. Leuckart 

 describes the embryo itself as " finely granular and armed at 

 the tip with a dagger-like spine, which, with the simultaneous 

 displacement of the adjacent granular mass, can be pushed 

 forward and drawn back again." Besides this so-called cephalic 

 granular mass, there are within the embryonic body two other 

 granular masses widely separated from each other, but occupy- 

 ing the posterior half of the embryo. These Leuckart supposes 

 to be the rudiments of a future brood, to be developed at the 

 time when the free embryo shall have lost its ciliated swimming 

 apparatus, shall have bored its way by means of the cephalic 



4 



