44 



STUDIES IN EVOLUTION 



32 



cup-shaped skeleton; as in Eucyrtidium elegans^^ Podocyrtis 

 Schomburghi^'^ Tridictyopus conicus^^ Cornutella hexagona^"^^ 

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

 orders probably originated according to I. In the Spumella- 



rian forms especially, the princi- 

 pal spines project from the prom- 

 inent portions; as in Trigonactura 

 triaeantha,^ Hymenactura coper- 

 nici^^ Rhopalastrum trieeros,^^ R. 

 hexaceros,^^ etc. The existence of 

 similar non-spinose species shows 

 that the formation of spines is in- 

 dependent of the growth of the 

 normal prominences; as in Rho- 

 palastrum malleus,^^ R. hexago- 



33 



35 



36 



7ium 



26 



etc. 



In the Foraminifera the con- 

 figuration of certain forms is such 

 that parts of the test are much 

 Figure 32. - Attheya decora, moi^e prominent than othcrs, and 

 a diatom, with spines from the in these cxposcd situations the 

 angles.- (From Mic^Dict.) -^^^ ^^^ ^^^^ frequently devel- 



Figure 33. — Diffluqia acumi- ^ . 



nata, a freshwater rliizopod ; opcd. Some of the triangular 

 showing spiniform projection of Tcxtulariai have spiucs at the two 



the fundus. X 200. (After Leidy.) , , . \, i -i 



Figure SA.-Diffliujia con- lateral angles on the oral side. 

 stricta, a freshwater rhizopod, Some of the individuals of Textu- 



TAftrTewJo^"''''"'" ^ '''■ ^«^*'^ folium^ show that similar 



Figure 35. — The same ; spines were developed at different 



showing a single spine on tiie gta^^es of jjrowth, SO that, in a full- 



fundus. X 175. (After Leidy.) ^ ^ . ' , ^ 



Figure 36. The same; show- grown specimen, there may be two 

 ing two spines. X 175. (After or three pairs of spines along the 

 ®' ^"^ sides. Others, like Verneullina 



spinulosa^ and Colivina pygmcea,^ develop spines from the 

 points of each chamber. A number of species, also, show a 

 single spine at the apex of the shell ; as Pleurostomella alter- 

 nans,^ Bolivina robusta,^ Folymorphina sororia, var. cuspi- 

 data,^ etc. In the latter species the ordinary form is rounded 

 or obtusely pointed at the fundus. 



