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XXXI.—The Life-History of Xenopus levis, Daud. By Edward J. Bles, B.A., B.Sc., 
Assistant in Zoology at the University of Glasgow. (With Four Plates.)* 
(Read January 18, 1904. MS. received January 11, 1905. Issued separately November 8, 1905.) 
INTRODUCTION. 
The present communication is intended to be the first of a series dealing with 
observations on the life-history of the Anura Aglossa and their anatomy at different 
stages of development. Xenopus levis, with its small ova and protracted larval 
free-swimming stages, must necessarily form a basis for the study of the develop- 
ment of that other remarkable Aglossan, Pipa americana. Although the adult 
Aglossan is an aberrant and specialised Anuran, there are Urodele features in the 
development of Xenopus which make its embryology of great general interest. 
These primitive features, combined with others peculiar to the genus, impress a 
character upon the early life-history of this frog which is widely divergent from 
that of the Phaneroglossa with small ova. 
The fullest account of the development of Xenopus is contained in a short paper 
by Bepparp, published in 1894. He has cited and reviewed the scanty earlier 
literature. Nothing has since been contributed to the subject but a note on the 
breeding habits by myself (1901). Brpparp’s observations were made on material 
obtained at the gardens of the Zoological Society of London. Specimens of Xenopus 
levis from Zanzibar spawned there a few months after their arrival. The earliest 
stage observed was the larva shortly after hatching; some frogs were reared from 
the tadpoles. The most important new fact made known in the paper was the 
presence of a cement organ (‘“‘sucker”). Its structure was described. W. K. Parker’s 
observations on the presence of external gills and the absence of so-called internal 
gills were confirmed. Some details of the internal structure were described. Figures 
drawn from fresh specimens are given of three tadpole stages, early and late. 
BEppaRp confirms the absence of horny teeth already noted by Parker (’76) 
and Lustre (90). But he did not connect this deficiency with the absolutely 
different method of feeding which must necessarily follow. The food of all our 
European tadpoles is obtained by the scraping action of the lips with their rows 
of horny teeth, sometimes, but rarely, aided by the biting horny jaws. The teeth 
act exactly like the radula of a gasteropod and are used to rasp away animal or 
vegetable matter from any substratum. Brepparp found numbers of Cyprids and 
nothing else in the alimentary canal of the Xenopus tadpoles, and concluded 
* Grateful acknowledgment is due to the Carnegie Trust for generously defraying the cost of reproducing the 
plates illustrating this paper. 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART III. (NO. 31). 116 
