44 



STUDIES IN EVOLUTION 



33 



36 



cup-shaped skeleton; as in Eucyrtidium elegans?* Podocyrtis 

 Schomburgki^ Tridictyopus conicus^ Cornutella hexagona^ 

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

 orders probably originated according to I. In the Spumella- 

 32 34 rian forms especially, the princi- 



vx x^88k P a ^ s pi nes project from the prom- 



[Jj inent portions; as in Trigonactura 



^jjjjjr triacantha Hymenacturacoper- 

 nici? Q Rhopalastrum triceros,^ R. 

 hexaceros, 2Q 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- 

 num^ Q etc. 



In the Foraminifera the con- 

 figuration of certain forms is such 

 that parts of the test are much 

 FIGURE 32. - Attheya decora, more prominent than others, and 

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



angles.- (From Mic^Dict.) { t f ntl d ^ 



FIGURE 33. D(fflugia acumi- * J 



nata, a freshwater rhizopod; Oped. Some of the triangular 



showing spiniform projection of Textularia3 have spines at the two 



thefundus. X 200. (After Leidy.) . 



FIGUBE M. D!fflugia con- lateral angles on the oral side. 



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

 Avith rounded fundus. X 175. 7 . /. 7 . Q i ,-> -i 



(After Leid ) IcLTia jolium y show that similar 



FIGURE 35. The same ; spines were developed at different 



showing a single spine on the t f growt h, SO that, in a full- 



fundus. X 175. (After Leidy.) 6 5 . 



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 Verneuilina 



spinulosa* and Colivina pygmoea^ 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, g Bolivina robusta^ Polymorphina sororia, var. c-uspi- 

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

 or obtusely pointed at the fundus. 



