100 FORMATION OF THE LAYERS. 



but in Amblystoma punctatum (Clark, No. 98), the male deposits the 

 semen in the water. The eggs are laid by the Anura in masses or 

 strings. By Newts they are deposited singly in the angle of a bent 

 blade of grass or leaf of a water-plant, and by Amblystoma puncta- 

 tum in masses containing from four eggs to two hundred. Salaman- 

 dra atra and Salamandra maculosa are viviparous. The period. of 

 gestation for the latter species lasts a whole year. 



A good many exceptions to the above general statements have been 

 i-ecorded '. 

 ( In Notodelpliis ovipara the eggs are transported (by the male?) into a 

 / peculiar dorsal pouch of the skin of the female, which has an anterior 

 I opening, but is continued backwai'ds into a pair of diverticula. The eggs 

 ! are very large, and in this pouch, which they enormously distend, they 

 \ undergo their development. A more or less similar pouch is found in 

 Nototrema marsupiatum. 



! In the Surinam toad (Pipa doraigera) the eggs are placed by the male 

 on the back of the female. A peculiar pocket of skin becomes de- 

 veloped round each egg, the open end of which is covered by a gelatinous 

 t>perculum. The larvse are hatched, and actually undergo their metamor- 

 phosis, in these pockets. The female during this period lives in water. Pipa 

 Americana (if specifically distinct from P. dorsigera) presents nearly the 

 same peculiarities. The female of a tree frog of Ceylon (Polypedates 

 , leticulatus) carries the eggs attached to the abdomen. 

 V Rhinoderma Darwinii^ behaves like some of the Siluroid fishes, in that 



I the male carries the eggs during their development in an enormously 

 developed laryngeal pouch. 



Some Anura do not lay their eggs in water. Chiromantis Guineeusis 



attaches them to the leaves of trees ; and Cystignathus mystacius lays 



them in holes near ponds, which may become filled with water after heavy 



rains. 



1 The eggs of Hylodes Martinicensis are laid under dead leaves in moist 



i situations. 



Formation of the layers. 



Anura. The formation of the germinal layers has so far only 

 been studied in some Anura and in the Newt. The following descrip- 

 tion applies to the Anura, and I have called attention, at the end of 

 the section, to the points in which the Newt is peculiar. 



The segmentation of the Frog's ovum has already been described 

 (Vol. I. p. 78), but I may remind the reader that the segmentation 

 (fig. 69) results in the formation of a vesicle, the cavity of which is 

 situated excentrically ; the roof of the cavity being much thinner 

 than the floor. The cavity is the segmentation cavity. The roof 

 is formed of two or three layers of smallish pigmented cells, and 



1 For a summary of these and the literature of the subject vide "Amphibia," by 

 C. K. Hoffmann, in Brouu's Classen uitd Ordnungen d. Thier-reichs. 



2 Vide Spengel, "Die Fortpflanzung des llhinodermaDarwinii." Zeit.f. wiss. ZooL, 

 Bd. XXIX., 1877. This paper contains a translation of a note by Jiminez de la Espada 

 on the development of the species. 



