Tlie Genus Synchceta. By C. F. Bousselet. 279 



power. I can see it best with my fine Zeiss apochromatic J s in. 

 water-immersion. 



Dr. Hudson enlarges upon the great difficulty in obtaining a 

 frontal view of Synchseta' s head. It is to be regretted that he did 

 not know the effect of a drop of 1 p.c. cocaine solution added to a 

 trough full of water. After a few minutes Synchseta, which Dr. 

 Hudson rightly calls " perpetual motion itself," becomes as quiet 

 as a dove, the body fully extended, the cilia moving, but with 

 gradually decreasing vigour until they stop altogether, remaining 

 thus narcotised and nearly motionless for more than an hour before 

 the animal dies. Moreover, some of them frequently fix their heads 

 to the cover-glass of the compressor and remain there for ten or 

 twenty minutes at a time, the cilia beating feebly all the time. 

 In this way I found no difficulty in obtaining ideal views of this 

 and other Synchsetse, usually in perpetual motion. 



The large mastax of Synchceta pectinata has a peculiar pear- 

 shaped form, characteristic of the genus, containing in particular 

 two finely striated V-shaped muscles embracing the base of the 

 long fulcrum. I have taken great pains to dissolve out the jaws 

 of 8. pectinata, which has proved a difficult task owing to the 

 extreme thinness and lightness of the parts. By mounting a 

 number of these separated jaws without pressure in a shallow cell, 

 I think I have succeeded in obtaining a correct interpretation of 

 their structure, which is shown in figs. 7 and 7a, front and side 

 view. The fulcrum a is a long narrow rod ; the rami b b are thin 

 elongated blades, ending in a single sharp tooth, with very thin, 

 curved, wing-like plates fixed to the sides ; the malleus consists of 

 a narrow curved manubrium c, from which also a very thin plate 

 of chitine projects, and a small triangular plate forming the uncus d. 

 The edges of the unci are quite smooth, and there are no teeth as 

 is the case in those of S. tremula, oblonga, gyrina, and others. 

 When looking at the unci from the dorsal or ventral side, a side 

 view is obtained, which of course gives the appearance of a single 

 sharp tooth. The shape and position of the parts will best be 

 seen from the figures. The snapping motion often seen in Synchseta 

 bears, I think, a different interpretation from that usually given to 

 it. Various authors have thought that the jaws protrude through 

 the mouth and seize their prey ; this, I think, is not the case, and 

 the snapping motion seen is due to a sudden opening of the buccal 

 funnel and cavity of the mastax, thus producing a strong sucking 

 action, just as in Asplanchna, which draws in the small algse, 

 infusoria, &c, forming the food of Synchseta. I have seen a pair 

 of tubular muscular bands attached to the dorsal side of the 

 mastax, just by the side of the spot where the oesophagus arises, 

 which may produce this action. The thin plates of the unci lie 

 exactly below the mouth, so that everything entering the mouth 

 can be seized by, and must pass between them. 



