500 The Embryology of Hylodes Martinicensis 



The development of the digestive tract has heretofore scarcely been 

 touched npon in the descriptions of the yolk-laden eggs. We have seen 

 a close similarity in the history of the yolk-mass in Hylodes and in the 

 few forms already studied, and the absence in Hylodes of a coiled 

 intestine. 



In the embryo of Hylodes, fed by the yolk in the egg; of Rhinoderma 

 darwinii, developed in the gular sac of the male; of Pipa americana, on 

 the back of the female; of Nototrema oviferum, in the dorsal pouch of 

 the female, no horny teeth or jaws have been found. (The presence or 

 absence of teeth is not recorded in the case of other protected embryos.) 

 It is also to be noted that no adhesive gland is found in Hylodes. 



Passing now to the organs of respiration, we find that different parts 

 of the body serve for breathing in different forms, and that there is great 

 diversity in the number and form of the gills, where present. 



In the viviparous salamander, the gills are finely feathered, and serve 

 for breathing in the fluid of the uterus. Larvae put into water do not 

 continue to use their gills unaltered; the gills either undergo certain 

 changes or are lost, and new gills or other organs develop. In Alytes, 

 the eggs are carried for a time on the hind legs of the male, and the 

 external gills are represented by one long branched pair. In Pipa 

 americana, in which the eggs are carried in water by the parent, 

 three pair of external gills develop, but these are lost early and 

 the internal gills appear. In Nototrema oviferum, in which the eggs 

 are carried in the dorsal pouch, one pair of bell-shaped gills occur, which 

 seem to represent two fused gills on each side. They are present before 

 the tadpole leaves the maternal pouch, and also for a short time after- 

 wards. A gill rudiment on the third arch may represent the internal 

 gills, but no others are present. In Nototrema marsupiatum, it is said 

 that there is no trace of external gills in the embryo when it leaves the 

 parent's pouch. Finally, the gills are entirely wanting in Hyla goldii, 

 whose eggs are carried on the back of the female; in Rana opisthodon, 

 whose eggs are found in crevices of rocks; in Rhinoderma darwinii, 

 vi'hose embryos are contained in the gular pouch of the male; and in 

 Hylodes martinicensis, whose eggs develop on land. In Hylodes even 

 the gill-slits are probably wanting. 



Respiration is carried on by some other means, which in some of these 

 cases has not been recorded. In Hylodes we have seen that the tail is 

 adapted to this function, i. e., the new function of breathing in air has 

 been assumed by an ancestral larval organ no longer useful in the 

 original way. In Rana opisthodon, the tail is not present in advanced 



