314 CRliSSWELL SHEARER. 



fibres, as in Stratiodril us, but they are but feebly developed. 

 A considerable prolongation of the blastocoelic cavity takes 

 place into the posterior limbs, running out along each leg 

 between the muscle-fibres and the glands. Into this space 

 the ova in the female are sometimes forced when the animal is 

 compressed under a cover-slip, sliowing that it is in free com- 

 munication with the cavity surrounding the gut. 



The movement of the limbs takes place alternately, the 

 head being swung from side to side with the movement of 

 the feet. It is a most remarkable sight to see the animals 

 rear up, as they sometimes do, on their hind feet, and stand 

 executing movements with their head while they remain 

 tirmly attached with their powerful hind feet. 'J'hey also 

 crawl quite readily, by means of the feet, on the underside of 

 the surface-film of the water. In the ordinary movements of 

 crawling the glands do not appear to throw out any secretion 

 on the pads of the feet; only when they are disturbed do 

 they pour out a thick secretion, which firmly attaches the 

 feet to the surface on which they happen to be. While the 

 animal violently twists its head and body, it never moves its 

 feet. This hold is remarkably firm. On the lobster ova the 

 parasites can be seized by the middle of the body by means 

 of a pair of fine forceps, under a dissecting microscope, and 

 the body pulled off, leaving the feet still attached, the limbs 

 having been torn from the body without loosening their 

 hold. 



As alreadv mentioned, the front limbs in Hi striobdella 

 differ from those of Stratiodrilus in that thev are non- 

 retractile. I have never been able to observe any retraction 

 of the feet in the living condition, or in preserved specimens 

 treated with different reagents. 



6. Digestive System. 



The digestive system is sharply specialised into a number 

 of divisions. These are readily seen in the figure of an 

 immature parasite (fig. 30). Here they are more marked 



