Lilian V. Sampson 477 



across the ventral surface. The chin is still very thick, and the hard 

 tip oi the upper lip persists. The tail is leaf-like and of considerable 

 size, though much smaller in proportion to the body than in previous 

 stages. The earlier observers record that the tail disappears during the 

 first day, or even within a few hours after hatching. The pigment of 

 the embryo in stage XIV is much denser than in preceding stages, but 

 is not arranged in the pattern characteristic of the adult. 



Stage XV differs externally from XIV in that the tail is reduced to a 

 small thick knob. 



If Hylodes be compared in external appearance with most of the forms 

 of the group to which it belongs, with Eana, for example, it is seen to 

 differ from the outset and throughout the immature stages much more 

 than in the adult stage. The egg differs not only because of its great 

 size, but in the absence of pigment. When the embryo of Hylodes first 

 appears, it is curved ventrally, like the embryo of a Ganoid, over the 

 bulky yolk, and obviously never has a dorsal flexure. When it begins to 

 show its true affinities, it resembles, in the shape of the head, in the 

 prominence of the eyes and in the presence of all four extremities, the 

 frog stage of Eana, rather than the larval tadpole. Only the holoblastic 

 cleavage and presence of the tail betray its relation to the larval form. 

 In short, the usual Anuran metamorphosis is replaced in Hylodes by a 

 direct development. The same fact is borne out by the internal characters. 



Ii: ORGANOGENY. 



The organogeny has been studied to some extent from dissections, but 

 for the most part from sagittal and cross sections. In so-called " cross 

 sections," the embryo, on account of its cur^^ature about the yolk, is not 

 everywhere cut transversely: the preparations have purposely been cut 

 in various planes through the lateral axis of the egg, in order to get 

 transverse and horizontal sections of different parts. (The left side of 

 the figure is in each case the right side of the embryo.) 



Owing to the large quantity of yolk in the younger embryos, it has 

 been difficult to prepare good series of sections. Eggs killed in Perenyi's 

 fluid are more readily saturated with paraffin and cut better than those 

 killed in picro-sulphuric acid or picric alcohol, but the most satisfactory 

 preparations have been obtained from specimens preserved in a fixative 

 containing picric acid and (after dehydration) left in cedar oil for about 

 12 hours, in cedar oil and paraffin about 5 hours, and in paraffin ( at a 

 melting point of 49° C.) about 8 hours. The sections can be cut of any 

 thickness from 5/x upwards. They were stained on the slide, because it 

 is difficult to orient the embryo in the microtome after surface staining. 



