210 DEVELOPMENT OF THE TADPOLE. 



one-half or a little further grown in which no movement could be 

 detected, but the blood-globules were seen lying perfectly still here 

 and there in the tissue. Suddenly, one of these gave a convulsive 

 throb, moved onwards slightly, retreated a little, then with a final 

 start moved forwards on its course, the rest following. Was this, 

 I wonder, the effect of the first true heart-beat which I observed, 

 giving an impulse to the whole of the globules throughout the 

 body, destined henceforth to act as carriers of nourishment to the 

 whole system? Possibly, however, it may only have been the 

 commencement of renewed circulation, which had been tempo- 

 rarily suspended on account of my own rough handling. 

 Whatever may be the correct explanation, the phenomenon was 

 most interesting and curious, having all the appearance of dead 

 and inert matter waking suddenly into life and continuing in that 

 life. 



To return to our diagram, we notice not only the branchial 

 arches with the gills, but also the hyoid {hy.), mandibular, and 

 trabecular arches. Another section of the mandibular arches is 

 shown in Fig. 6, Plate XIII., where they are seen supporting the 

 mouth cavity {m.c). 



It will be remembered that these observations were primarily 

 undertaken to obtain if possible some definite information on the 

 food of the tadpole. Reference to Figs, i, 2, and 3, Plate XIII., 

 as well as to Figs, i and 5, Plate XX., will show that, although up 

 to March 23rd, the date of these sections, the mouth cavity was 

 well formed, yet the animal could not possibly eat, as the mouth 

 was not only closed, but perfectly covered with the epidermis, 

 although the papillffi on the labials had commenced to form, as well 

 as the salivary glands at the sides of the mouth. Up to this date 

 it will, therefore, have been manifestly impossible for these embryos 

 to have obtained food through the mouth, as mouth there was 

 none. Nourishment, however, must have been obtained; for 

 during the month now elapsed, the eggs had increased both in 

 weight and bulk, and as we have seen, had become so wonderfully 

 altered in form that there was now no resemblance to the original 

 spherical contour. All nourishment would, therefore, up to this 

 date, appear to have been imbibed from the water through the 

 epidermis ; but in a few days — namely, by March 29th — the lips 



