G E. Beecher — Origin and Significance of Spines. 251 



32 



M 



flattened miter-shaped form with a distinct edge, along which 

 are numerous spines. It should be noted that no spines are 

 developed on any portion of these fresh-water Rhizopods 

 except those here mentioned. 



The Nasellarian Radiolaria furnish many instances of a 

 terminal spine from the summit of the silicious helmet or cup- 

 shaped skeleton, as in Eucyrtidium elegans™ Podocyrtis- 

 Schomburghi™ Tridictyopus conicus,™ Gornutella hexagona,™ 

 etc. Many of the primary, or axial, spines in other sub-orders 

 probably originated according to I. In the Spumellarian forms 

 especially, the principal spines project from the prominent por- 

 tions, as in Trigonactura tria- 

 cantha™ Hymenactura copernici™ 

 Rhopalastrmn triceros,' 26 R. hexace- 

 ros™ etc. The existence of similar 

 non-spinose species shows that the 

 formation of spines is independent 

 of the growth of the normal prom- 

 inences, as in Rhopalastrum mal- 

 leus™ R. hexagonum™ etc. 



In the Foraminifera, the configu- 

 ration of certain forms is such that 

 parts of the test are much more 

 prominent than others, and in these 

 exposed situations, the spines are 

 most frequently developed. Some 

 of the triangular Textulariae have 

 spines at the two lateral angles on 

 the oral side. Some of the indi- 

 viduals of Textularia folium* show 

 that similar spines were developed 

 at different stages of growth, so 



33 



35 



36 



that, in a full grown specimen. 



there may be two or three pairs of 

 spines along the sides. Others, like 

 Verneuilina spimdosa 9 and Coli- 

 vina pygmma 9 develop spines from 

 the points of each chamber. A 

 number of species, also, show a 

 single spine at the apex of the shell, 

 as PleurostomeUa alternans 9 Bo- 

 livina robusta, 9 Polymorphina ™8j™ s P ines 

 sororia, var. cuspidata 9 etc. In 

 the latter species, the ordinary form is rounded, or obtusely 

 pointed at the fundus. 



Some of the Infusoria have terminal spiniform processes, 

 which, by analogy with other forms, have probably developed 

 according to I, as Geratium tripos 9 G. longicome 9 G fusus 9 



Figure 32. Attheya decora, 

 a Diatom with spines from the 

 angles. (From Mic Diet.) 



Figure 33. Difflugia acumi- 

 nata, a fresh- water Rhizopod. 

 showing spiuiform projection of 

 the fundus, x 200. (After Leidy.) 



Figure 34. Difflugia con- 

 stricta, a fresh-water Rhizopod, 

 with rounded fundus. x 175. 

 (After Leidy.) 



Figure 35. The same, show- 

 ing a siDgle spine on the fundus, 

 x 175. (After Leidy.) 



Figure 36. The same, show- 



xl7 5. (After 



Leidy.) 



