31 
seven in Pipa. Srannius (39, p. 130) says that in Pipa the first 
vertebra is fused with the second, and that the sacral is fused with 
the urostyle, and that the latter fusion occurs in Xenopus. By his 
use of the word “latter” it is evident that he intends to convey the 
impression that the first two vertebr& of Xenopus are free. MıvArT 
(29, p. 295) and Corr (10, p. 253) state definitely that the first two 
vertebree are separate in Xenopus. VON JHERING (25, p. 299), how- 
ever, observes that the anterior end of the vertebral column of Xeno- 
pus has undergone a modification similar to that of Pipa, and 
(p. 297) that the first spinal nerve penetrates the first vertebra of 
Xenopus as it does that of Pipa. And Horrmann (21, p. 57) and 
PETER (34, p. 571) also maintain that the first two vertebre of Xeno- 
pus are fused, as in Pipa. ADoLPHI includes Xenopus in his 
list of Anura exhibiting a fusion of first and second vertebra, but 
with the following qualification (1, p. 363), — “bei Dactyletra 
(Xenopus) ist die Verwachsung von Wirbel I und II nicht absolut 
konstant”, and herein, I take it, lies the explanation of the numerous 
contradictory statements. It would be a most valuable addition to 
our knowledge if the percentage of fusions in a very large number 
of specimens of Xenopus were worked out in the same manner and 
with the same thoroughness as ApOLPHI has already done for Bufo 
variabilis, Pelobates fuscus and Bufo cinereus. I have 
only been able to examine nine skeletons of Xenopus, but in all 
of these the first two vertebrz were distinct. In none of the numerous 
Xenopus larve, also, which I have examined did I find any con- 
fluence of these vertebre. 
Pipa is by no means the only Anuran in which the coalescence 
of the first two vertebr& is met with. It occurs regularly in Palxo- 
batrachus (41, Teil 1, p. 29), and very frequently in Ceratophrys, 
Breviceps and Brachycephalus (1, p. 362). Corps (9, p. 108) 
states that a similar union occurs in Pelodytes, but it is evident that 
the specimens on which the observation was based were abnormal. 
In Pelobates Avorepnr (2, p. 473) found the first two vertebra fused 
in 8 cases out of 65, i. e. in 12,3°/, of the skeletons examined, and 
he leans to the view that this confluence is a relic of an ancestral 
condition in which the two vertebr& were normally and regularly united. 
In the genera Rana and Bufo the first two vertebre are distinct, 
but several cases of abnormal confluence of these vertebrae have been 
described within the last few years by Anporput (B. variabilis, 
1, p. 351—353 and p. 367; B. cinereus, 3, p. 122—123; R. escu- 
lenta, 2, p.485), Howes (R. Guppyi and R. catesbiana, 24, p. 270) 
and BEnHAM (R. catesbiana [mugiens] and B. agua, 5, p. 477). 
In a side view of the developing vertebral column of Xenopus 
