330 C. K Beecher — Origin and Significance of Spines. 



I.) They are also quite frequent among the Echinoidea, but 

 more rare among the Asteroidea and Crinoidea. 



Compound antlers are especially characteristic of the modern 

 Deer family, though compound horns are but rarely found 

 elsewhere among the mammals. The Prong-horn Antelope of 

 America is the only living species of hollow-horned ruminant 

 having this character. It, of course, is not intended that extra 

 pairs of horns, which being separate, and often originating on 

 different portions of the skull, should be considered as com- 

 pound horns in the sense employed here. Likewise compound 

 spines arising through suppression of organs or structures are 

 not to be included here, as the compound thorns on the Honey- 

 locust representing aborted branches. 



51. 



52. 



Figure 51. Acontaspis hastaia. A Radiolarian, showing multiplication of 

 spines by repetition, x 200. (After Haeckel.) 



Figure 52. Strophalosia keokuk. An attached Brachiopod, showing the 

 spines extending from the ventral valve to and along the surface of attachment. 

 x2. 



Figure 53. A Gastropod shell (Platyceras) to which are attached a number of 

 Strophalosia keokuk. Natural size. 



The fin-spines of fishes are often compound, and sometimes 

 are made up of several elements as in the spines of Edestus (E. 

 vorax). Quite a number of Mollusca develop compound 

 spines, as in many species of Spondylus and Murex. They 

 are also not uncommon among the Crustacea and Insecta. 

 Compound spines are infrequent in the Brachiopoda, being 

 developed in but few species (Spirifer hirtus 91 ). The For- 

 aminifera also present but few examples (Polymorphina 

 Orbignii ). 



