26 ILLINOIS BIOLOGICAL MONOGRAPHS [26 



trabecula and reaching farther forward than before (Fig. 21). Anterior 

 to the crista, each trabecula turns more abruptly toward the median line for 

 a short distance, and then anteriorly; uniting by a very small planum bas- 

 ale, which in this stage is flat and level, with the dorsal surfaces of the 

 trabeculae. 



Anterior to the planum basale, the trabeculae continue forward, sep- 

 arated from each other by a narrow internasal space; each expands distally 

 into a small cornu which supports the tip of the nasal organ. Arising from 

 the dorsal and medial margin of each trabecula, just anterior to the planum 

 basale, is a small process which extends backward a short distance along the 

 medial margin of the nasal sac. This process is the further development 

 of the medial ridge of the trabecula in the 37 mm. stage; and from its 

 relation to the nasal organ, it must be the beginning of the columna 

 ethmoidalis, whose further history is unknown (Fig. 61). 



I regret that I have no older stages showing the farther chondrification 

 of the capsule; thus preventing a careful comparison with other Urodeles. 

 In general, however, Spelerpes seems to indicate a retarded growth in all 

 parts. In corresponding ages of other Urodeles, there is a much more 

 complete capsule than in Spelerpes. 



I have not observed the free anterior extension of the crista in any 

 other Urodele, with the exception of Amphiuma; and judging from its 

 relation to the nasal organ and trabecula, it would appear as though this 

 process is the posterior beginning of the ethmoidal column. In other 

 words the columna ethmoidalis in Spelerpes may arise by the fusion of two 

 parts independent of each other; the anterior part from the medial margin 

 of the cornu, the posterior part from the anterior margin of the crista. In 

 no other Urodele, as far as I have seen, does the column arise in just this 

 way; however the early development of the crista trabeculae in Crypto- 

 branchus and the lateral development of the tectale from the middle of 

 the ethmoidal column, leads me to conclude that in Cryptobranchus the 

 column arises, as in Spelerpes, from two distinct independent outgrowths. 



The small planum basale is similar to that in Cryptobranchus, but the 

 larger cornu in the 37 mm. stage is more like that of Amblystoma. My 

 material does not show the formation of the planum verticale, but it 

 evidently does not arise as a dorsal growth from the planum basale, but 

 more probably by medial growths from the ethmoidal columns; thus in 

 this particular, approaching the condition in Salamandra. 



The complete absence of intermaxillary glands, the close approxima- 

 tion of the capsules anterior to the planum basale, as well as the small size 

 of the latter, are points of similarity to Cryptobranchus, which, on the 

 evidence of larval characters alone, I believe Spelerpes more closely resem- 

 bles. 



