NATURAL HISTORY OF BRITISH SALMONID&. 137 



interested in this curious discovery of a fish-eating weed, secured 

 another specimen of Utricularia, and put it into a separate vessel, 

 with fresh spawn and young fry of roach. In about six hours more 

 than a dozen of the fish were found caught in the wee green gins. 

 In most cases the fish are caught by the head ; and when this is so, 

 the snout is pushed into the bladder as far as it will go, till it touches 

 the opposiie wall, leaving the tail of the poor struggling thing half 

 free outside. Sometimes, however, the bladders catch the young 

 roach by the tail, a fact which seems to prove the truth of Mrs. 

 Treat's view that the valve actually snaps at the prey, instead of 

 merely allowing it to enter passively. In one of Professor Moseley's 

 specimens, a fish was caught by the yolk bag, which fry carry in 

 their early stage attached to the stomach ; and in another instance 

 two bladders had got hold of the same fish, one trapping him by 

 the head and the other by the tail. 



Seen under the microscope the semi-transparent green traps, 

 with the tiny silvery bodies of the dead fish half protruding from 

 them, form very striking and beautiful objects. The big black eyes 

 of the fish show out clearly by transmitted light through the green 

 wall of the cell that has caught them. Preserved in spirits, the 

 specimens are less interesting, because then the bladder loses its 

 green colour, and the force of the contrast is considerably weakened. 

 After the fish have been for some time trapped they assume a slimy 

 deliquescent appearance, and are rapidly absorbed by the glandular 

 processes. As these processes project obliquely backward, Pro- 

 fessor Moseley thinks it probable that they help to catch the fish 

 and prevent him from escaping, in somewhat the same manner as 

 the barbs of a hook or arrow, or as the backward-pointing twigs of 

 an eel buck would do. Each fresh struggle and plunge must make 

 the fish get deeper and deeper entangled in the trap, because the 

 processes, catching in his gills or gill slits, prevent him from moving 

 backward and compel him to move forward only. Vestigia nulla 

 rctrorsum. 



One word as to the evolutionary history of this singular water 

 weed. It is a close relation of the beautiful pale-green butterwort, 

 whose graceful purple-blue blossoms are found on almost every 

 upland bog or hilly brookside along the whole western half of our 

 islands. Butterwort is itself an insectivorous plant, as are all its 

 congeners ; and Utricularia is only a butterwort which has taken 

 to living in water, and has so far adapted itself to its new condi- 

 tions as to eat fish as well as insects. By descent, the butterworts 



