BCHINORHYNGHUS. 103 



tlie whole interior of the embryo." After this, the sexual diffe- 

 rences become clearly established, and the now narrowed 

 original space between the surface of the young Echinorhyn- 

 chus and the body of the embryo becomes transformed into 

 a series of anastomosing canals, constituting the so-called 

 water-vascular system — to which allusion has already been made 

 in my account of the general anatomical features of the adult 

 worm. The lemnisci make their appearance at a late period, and 

 the nature of their connection with aquiferous system is a point 

 which still remains unsolved. Leuckart further remarks that the 

 passage of the young Echinorhynchi into their ultimate piscine 

 hosts is probably unattended with any very striking structural or 

 morphological changes, whilst the metamorphosis of the embryo, as 

 thus far detailed, occupies a period of about six weeks. In general, 

 the crustacean hosts appear to suffer little from the borings of the 

 embryo parasites ; but when the latter have assumed the Echinor- 

 hynchus condition and happen, at the same time, to be particu- 

 larly numerous, then they not unfrequently prove fatal to the un- 

 suspecting Grammari. Leuckart informs me that after their trans- 

 ference into the intestine of the ultimate host, a period of about 

 one week more is required to complete their development. 



