266 C. E. Beecher — Ori<jh> anil Sh/ nip '■«,<<■< <>f Spines. 



long spine, dilated at the base into a crest, and carrying a long 

 forked appendage. The back is arched, and on the under side 

 are two deep indentations. The .-pines on the ridges of the 

 shields are the strongest ; they are compressed, are not flexible, 

 and each terminates in a pair of short points. There is one 

 pair of these spines in the middle of the back, and one on each 

 of the three prominences of the abdominal outline; they 

 terminate in flaps, which are long and forked. There are also 

 very long compressed flexible spines without appendages, 

 which extend in pairs along the uppermost part of the back. 

 while a single series extends along the middle line of the belly. 

 Small short conical spines run in a single series along the 

 middle line of the sides,, and along the lateral in\^> of the 

 belly ; and there is a pair of similar spines in front of the ba>e 

 of the pectoral fin. The tail, which is about as long as the 

 body, carries the dorsal fin; it is quadrangular, and has sharp 

 edges. It carries along its upper side five pairs of bandd:>ear- 

 ing spines, which terminate in branching filaments." * 



The Horned Toad Phrynosoma bears considerable resem- 

 blance to the joints of the Prickly Pear, with which it is often 

 associated, and it may be suggested that the likeness both in 

 form and spinescence represents mimetic characters. 



VI. Prolonged development under conditions favorable for multi- 

 plication. (B,.) 



The prolonged development or existence of a stock under 

 favorable conditions for multiplication may be considered as 

 one of the primary influences favoring the production of 

 spines. This implies abundance of nutrition and compara- 

 tively few enemies outside of other individuals of the same or 

 closely related species. Under a proper amount of increased 

 nutrition, the vitality and reproductiveness of a stock are 

 raised,- and other things being favorable, it is found that the 

 stock will give expression to what has already been described 

 as free variation. Hypertrophy is also very apt to be one 

 result of abundant nutrition, so that structures of little or no 

 use may be developed, and some of them comprise certain 

 features which are often called ornamental. 



In the excessive multiplication of individuals, it is evident 

 that there must be a great number of natural variations, and 

 that some of these will affect the pairing of the sexes in such a 

 manner as to accentuate and delimit certain variations. Even- 

 tually, there also comes a struggle for existence in which favor- 

 able modifications have a decided advantage. In this way, it 



* The artist who copied Gunlher's figure for Lennis " Synopsis der Thierkunde," 

 3d ed., by H. Ludwig (vol. i. p. 770, 1883) connected the fish with the adjacent 

 fronds of seaweed so as to form a single organism. 



