4 DB. W. G. EIDEWOOD ON THE [Jan. 18, 



The following papers were read : — 



1. On the Development of the Hyobranchial Skeleton of 

 the Midwife-Toad {Alytes ohstetricans) . By W. G. 

 RiDEWOOD, D.Sc, F.L.S., Lecturer on Biology at 

 St. Mary's Hospital Medical School, London. 

 [Eeceived November 15, 1897.] 

 (Plate II.) 



The object of the present investigation was to ascertain how 

 far the peculiarities of the hyobranchial development of Pelochjtes, 

 already detailed in the Proceedings of this Society (9), are to be 

 considered normal for phaneroglossal Anura generally. The adult 

 hyobranchial skeleton of Pelochjtes is so aberrant in structure that 

 it is natural to suspect that the mode of development of the parts 

 may not conform very closely with that of a more generalized type 

 of Anuran. Since the arciferous type of shoudler-girdle, the 

 presence of free ribs, the frequent persistence of postcardinal 

 veins, and the primitive nature of the carpus and tarsus show 

 Alytes to be one of the most lowly organized of the Anurous 

 Batrachians, and in consideration of the larger size of the tadpoles 

 of this genus as compared with those of the otherwise equally 

 suitable genus Discor/lossus, Alytes was chosen to supply the test. 



The material for the investigation was, as before, generously 

 provided by Mr. G. A. Boulenger, E.E.S., of the Natural History 

 Museum, London. Twenty-one specimens were dissected, and 

 from these the eight here described and figiu'ed were so selected 

 as to exhibit the most even gradations from the youngest stage to 

 the adult condition. The stages are numbered 1-8 to distinguish 

 the order in which they succeed one another ; but the use of these 

 figures does not imply correspondence with any stage bearing a 

 similar number in the previous descriptions of the hyobranchial 

 skeleton of Xenojms, Pipa (8), and Pelodytes (9). In order to 

 facilitate comparison the figures are not drawn to the same scale, 

 but as nearly as possible of the same absolute size. The approxi- 

 mate magnification is given in each case. Figures 1-7 exhibit 

 the dorsal surface of the hyobranchial skeleton, but fig. 8, of the 

 adult, is drawn from the ventral surface, so that the ventral 

 splint-bone may be more clearly seen. The method of procedure 

 was the same as in the two earlier investigations ; and as the 

 nomenclature of parts adopted in this paper is the same as that 

 previously employed in the description of the hyobranchial 

 apparatus of Pelodytes, a lengthy introduction is here unnecessary, 

 The adult skeleton of Alytes (Plate II. fig. 8) is not very 

 remarkable. The hyoidean comua {h) are thin and continuous, 

 but rather more flattened than in the Common Prog. The 

 posterior comua or thyrohyals (t) are normal, and in the middle 

 of the ventral surface of the body of the hyoid is a V-shaped 



