68 /. H. Poivcrs 



considerable interval often intervening, especially between the 

 two anterior groups. The teeth can no longer be described as 

 forming "combs," but are now in broad ovate "brushes.'' Even 

 the posterior groups which in the normal larva were arranged 

 in an almost perfect series of but one tooth in width, are now ar- 

 ranged in a brush in such a manner that straight rows of teeth 

 run diagonally across the brush ; and the middle rows show four 

 teeth each, and wide apart. In the anterior brushes the teeth are 

 also arranged in regular diagonal rows and show at least six teeth 

 to some ji the rows. Most conspicuous of all is the extent to 

 which the two anterior groups of these palatine teeth, and espe- 

 cially the biructures which bear them, come to project downward 

 into the mouth. The posterior brushes remain more nearly at 

 their old level, but the anterior brushes project downward — not 

 only the teeth, but the supporting structure — until there is actu- 

 ally a constriction about the bases of the entire structure as if it 

 were being separated ofit" from the palate upon which it is borne. 

 So great is this hypertrophy of teeth and tooth-bearing structure 

 that in looking straight into the animal's mouth — the line of 

 vision passing the upper jaw straight to the throat — not only 

 the teeth but even the pad which bears them projects visibly be- 

 low the upper jaw, and bears on each side a formidable array of 

 lance-pointed teeth. As one looks into the mouth, six or seven 

 such teeth show on each side. As to the actual change in the size 

 of the teeth, measurements are difficult, but a fair idea is gained 

 by the following: before me, as I write, lie the upper jaws of 

 two 10 cm. larvae, a daphnid-feeder and a cannibal. In the for- 

 mer I can not see the separate teeth, even under water, with the 

 naked eye. With a Hastings lens of fifteen diameters I can see 

 most of them on one side ; to count the exact number is difficult ; 

 I require to turn the head, and to light each side very favorably 

 before I can see even the majority of them. In the cannibal head 

 I can see many of the separate teeth with the naked eye at a dis- 

 tance of two feet, and all of them, so far as they project out- 

 wardly in plain view, by closer scrutiny. I judge, then, that these 

 teeth are, in size and free projection, not less than thirty times 

 as large as the others. 



264 



