476 BUMPUS. (Vou. XII. 
vertebra is bi-convex; but in this case it is the twenty-eighth, 
in the other the twenty-seventh. Is it not evident, therefore, 
that at some place between the occipital condyle and the first 
caudal a new vertebra has been inserted? By careful compari- 
son I find that this new vertebra has been intercalated between 
the ninth and tenth.” 
Dr. Baur does not tell us how he was able to pronounce this 
an intercalated segment, leaving it to be presumed, however, 
that a new vertebra possesses certain diagnostic features. 
Moreover, if perfectly formed sacral ribs may appear through 
discontinuous variation on the XX vertebra of the “ mud- 
puppy,” I see no reason why the new first caudal of the abnormal 
gavial should not produce a bi-convex rather than a proccelous 
centrum. 
If we could only have the relative trunk and tail measure- 
ments of these specimens with abnormal vertebrz, and could 
compare them with the normal, we could soon tell whether a 
strange vertebra had been wedged into the regular series, 
making the trunk abnormally long, or whether the arrest in 
the development of a trunk vertebra had not resulted in the 
abortion of certain anterior vertebra, drawing into the sacral 
region certain primarily caudal elements. 
The Helodermas mentioned by Baur, on page 335, would form 
excellent material for such a comparative study, since the four 
specimens exhibit four variations in the numerical position of 
the first caudal vertebra. But in the absence of a large number 
of Helodermas, let us examine again our Necturus material 
and see if we cannot find vertebre that might be looked upon 
as intercalated. 
Specimen No. 46 shows a slight reduction in the lengths of 
the fifth and sixth vertebra, and specimen No. 61 shows a 
similar reduction in the twelfth and thirteenth. In both cases, 
the posterior of the affected vertebrz is slightly smaller than 
the anterior. 
If during the process of embryonic growth there was a dis- 
turbance of the regular formation of the body segments, we can 
easily see that this disturbance might have resulted in the 
interruption of the growth of certain pre-sacral vertebre. The 
SS = = —_— 
a ee 
2S SS 
—T 
Sa 
