18 THE LESSON OF EVOLUTION 



discovered by Dr. C. Barrois, in Brittany, should 

 be placed in it. 



The animal origin of Dr. Cayeux's specimens has 

 been doubted by some palaeontologists ; but , if we 

 may rely on the accuracy of the published figures 

 which has not been challenged they certainly 

 appear to be Kadiolarians and sponge spicules. The 

 figures of the Foraminifera seem more doubtful. 



The Kadiolarians are very minute, about one- 

 fifteenth of the diameter of similar forms in 

 Cambrian and younger rocks. Most of them have a 

 thin spherical shell pierced with holes, and are 

 sometimes furnished with spines ; but the forms are 

 various. Twenty-four genera have been distin- 

 guished, two-thirds of which are still living; and 

 there are many others, the genus of which cannot 

 be determined, although they are unquestionably 

 Kadiolarians. By far the commonest forms belong 

 to Gerosphara, a still living genus, known also in the 

 Silurian period, which belongs to the legion 

 Spumellaria, the fundamental form of which is 

 spherical or ellipsoid. But the legion Nassellaria, 

 in which the fundamental form is ovoid, is also 

 represented by nine genera, although the individuals 

 are not so numerous as those of the first legion. 



Sponge spicules are probably common, but they 

 are generally broken. They belong chiefly to the 

 simple forms of Monactinellidae, or to the Lithisticlse , 

 or the Tetractinellidae ; but a few fragments be- 

 longing to the Hexactinellidse have been recognised. 

 Many are of branched or radiate type, and they are 

 surrounded by pyrites, which probably represents the 



