DEVELOPMENT OF THE TADPOLE. 151 



In the whole of our sections there will be seen, on the under 

 part of the head, a dark mass, cl. — called the claspers — an en- 

 larged horizontal section of which is given in Fig. 7. They are 

 hollow bodies, evidently outgrowths of the epidermis. The 

 central cavity is bounded internally by a row of very small, dark 

 cells, and radiating from these are larger, elongated, black cells, 

 ■which stretch in fairly parallel masses nearly to the outside of the 

 structure, the whole being covered by the polygonal cells of the 

 epidermis. The two parts of which they are composed approxi- 

 mate very closely to each other, if they are not, indeed, in actual 

 organic connection, by means of the epidermis, but at a certain 

 period of their growth they are distinctly separate. Although these 

 commonly -called claspers are referred to by embryologists as suc- 

 torial discs, I cannot find any opening into the interior whereby 

 suction can be carried on by them. Nevertheless, that such an 

 opening exists would appear probable, unless, indeed, they are not 

 suctorial discs at all, but claspers in the true sense of the word. 

 From the yelk being situated in the abdominal region, combined 

 with the cavities in the head, the animal must necessarily take an 

 inclined position in the w-ater, head uppermost, whilst the compara- 

 tively great weight of the abdominal regions drags the animal down- 

 wards in the water. The claspers will now press laterally on any- 

 thing, as, e.g., parts of the gelatinous envelope or external objects, 

 which may mechanically find their way between them, the animal 

 being merely held in position by the combined effects of the 

 greater specific gravity of its lower parts and the slight adhesion 

 which takes place between the so-called suctorial discs. 



EXPLANATION OF PLATE XIII. 



Figs. 1 — 5. — Sections from one Tadpole, taken March 17tli. 

 ,, G. — Mandible arches. 

 , , 7. — Claspers, 

 ,, 8. — Pro-renal Ducts and Lungs. 



Sp.c, spinal cord ; ?ic., notochord ; m.c, mouth-cavity ; h., heart ; 

 St., stomach ; al., alimentary tract ; ca. , cloaca ; cZ. , claspers ; I., liver ; 

 e.b., elastic band, surrounding notochord and spmal cord ; pni., pro- 

 neplnx>3, or immature kidney ; sh., sheath of ditto ; m.h., mandibular 

 and hyoid arches ; 0. , optic vesicle ; ati. , auditory capsule ; b. , brain ; 

 ep. , epidermis ; pn. , pineal gland ; ga. , ganglia. 



