336 C. E. Beecher — Origin and Significance of Spines. 



to interpret a vestigial or suppressed structure directly into 

 terms of an unfavorable environment. Thus, if the probable 

 origin of the vestigial hind legs of a Python is considered, 

 it leads to the belief that they represent legs which were of 

 functional importance to some of the early ancestors of this 

 snake. The gradual elongation of the body and the consequent 

 change from a walking or direct crawling habit to a mode of 

 progression chiefly by horizontal undulations, necessarily 

 brought the legs into a relation with the environment which 

 was unfavorable either for their function or growth. Their 

 suppression is complete in most snakes, but in the Python, 

 the hind legs are represented by two spurs or spines (figure 

 58). On the interior of the body they are supported by ves- 

 tiges of femora and ilia, showing their true affinities with hind 

 limbs. Some snake-like Batrachians (as Am/phiuma and Pro- 

 teus) still retain short and weak external limbs. These would 

 undoubtedly soon be lost by a change from aquatic to terres- 

 trial or arboreal habits. 



58. 59. 



Figure 58. Portion of skin of Python, showing the spurs which represent 

 the suppressed or vestigial hind legs, x \. (After Romanes.) 



Figure 59. Bones of suppressed legs of Python. All but the claw-like 

 termination are internal, x \. (After Romanes.) 



In explanation of the nodes and spinifor'm processes on the 

 epitheca of Michelinia favosa, it may be suggested that they 

 represent aborted corallites, or attempts at budding. This 

 coral belongs to the order Porifera, which has been shown by 

 the writer 7 to have very pronounced tendencies toward pro- 

 liferation, and on the interior of the colony, these attempts 

 result in the production of mural pores. Most of the species 

 of Michelinia are hemispherical or spherical. M. favosa is 

 inclined to be pyriform in shape, rising above the object of 

 support, and thus presenting a rather large epithecal surface. 

 Manifestly the lower side of the corallum is unfavorably situ- 

 ated for the growth of corallites, and any efforts at prolifera- 

 tion on the part of the peripheral corallites is apt to result in 

 stunted outgrowths. There is here a very close connection 



