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ovigerous tube and the diameter of the tube, we can calculate 

 the number of eggs contained in any portion of the tube. 

 This organ is folded up in every direction in the interior of 

 the body, so that in the breadth of the body it crosses and 

 re-crosses six or eight times. With these data I have been 

 able to estimate approximately the number of the eggs con- 

 tained in a piece of the worm of a decimetre in length at 

 six or seven millions. One can judge in this way of the total 

 number of eggs Avhicli the animal can contain at one time in 

 the interior of its body. 



The egg presents a very thick shell of a chitinous charac- 

 ter, the colour of which varies from yellow to dark brown. 

 The dehiscence of the egg takes place by the formation, near 

 one of its poles, of a circular crack always very regular, 

 which divides the shell into two very unequal portions (PL 

 YIII, figs. 2 and 6). It is the manner in which the eggs 

 burst in the majority of Trematods. 



The length of the body of the embryo measures nearly 

 double the long axis of the egg in which it is folded up, bent 

 at its middle in such a way that the posterior half of its body 

 is found to be applied against the anterior half. Its average 

 breadth is about equal to half the breadth of the small axis 

 of the egg. Its body is of an elongated form, and draws itself 

 slowly along from before backwards. In front it is furnished 

 with a distended part, probably of a muscular nature, on 

 which a crown of bristles or booklets is implanted, the form 

 and disposition of which are very remarkable. 



The anterior enlargement of the body, which we will call 

 the muscular disc, is naturally divided by two diameters, 

 cutting each other at right angles, at the centre of the disc, 

 into four sectors, which are nearly equal. The form and 

 disposition of the hooklets is the same in two opposite sectors, 

 different in two adjacent sectors. If we were dealing with 

 a crystal, Ave should say that it presented a bilateral 

 symmetry. 



In each of the sectors A and B (figs. 4 and 8), we counted 

 seven hooklets, of which four larger are separated from one 

 another by three others, which arc smaller. All are arranged 

 in a radiating manner on the disc, and diverge from the 

 centre to the periphery. All these hooklets are nearly- 

 straight. The large ones present, nevertheless, in one point 

 a slight enlargement, which gives them a certain re- 

 semblance to the bristles characteristic of the six-hooked 

 embryo of Cestoids. I was not able to recognise the presence 

 of this median swelling in all the individuals which I have 

 observed, but that may depend on the position of the hook- 



