.-.^ 



478 The Embryology of Hylodes Martinicensis 



Eggs that are well preserved in formalin, make fairly good sections and 

 can be readily cut after two or three hours in paraffin. 



1. Origin of Organs. 



My material is insufficient to more than suggest a few points in regard 

 to the origin of the organs. 



Sections of an egg of the stage of Fig. 5, showing the thick lips of the 

 blastopore and the large yolk plug, and sections of a later stage, where the 

 yolk plug is reduced and receding, are similar to sections of the corres- 

 ponding stages of Eana. In sections of stage I (Fig. 6), the neural plate 

 is solid, recalling the condition in Teleosts and bony Ganoids. 



The notochord appears in a few sections in the posterior region of an 

 embryo of stage II as an evagination of the dorsal wall of the archenteron 



(Fig. A, n) and the same 

 condition is indicated in 

 younger eggs. Anterior to 

 the section shown in Fig. 

 A the entoderm is continu- 

 ous over the archenteric 



Fig. A. Cross section of stage II, through the pos- cavity, ventral to the noto- 

 terior part of the embryo, to show the origin of the 



notochord. ac, archenteric cavity; n, notochord; y, chord, but posterior to this 

 yolk-mass. '- 



section the entoderm does 

 not appear to be continuous ventral to the notochord." 



2. Digestive Tract. 



a. Alimentary Canal. — In stages midway between the first and last of 

 the series, the chief organs derived from the archenteron are definitely 

 established, and the alimentary tract is clearly divided in relation to the 

 yolk-mass, into three regions, anterior, posterior and middle (see Fig. F). 



At an early stage, the broad low archenteric cavity is continuous from 

 one end of the embryo to the other (stage II, Fig. Bl, ac). The floor 

 of the cavity is the enormous yolk-mass, which is met abruptly at the 

 sides by the thin roof of entodermic cells filled with yolk. 



In the same stage (II, Fig. Bl), the mesoblast is beginning to separate 

 into splanchnic and somatic layers; as the process continues and the 

 coelom (Fig. Bl, 2 be) increases, the lumen of the archenteron becomes 

 narrower (Fig. B2, ac), and in the middle region it is completely oblit- 



^Cf. Bufo lentiginosus, where the conditions are similar, except that one 

 layer only is contributed by the chorda-entoderm to the notochord in the 

 middle region of the embryo. — King, 03. 



