40 SYNOPTIC COLLECTION. 



uct of the fission becoming encysted within the shell. 

 Fig. 8 shows four cysts, which in time are ruptured, 

 allowing the embryos to slip out. 



The process of development observed by Hertwig l 

 differed somewhat from the above. He saw the division 

 of the body with the formation of flagellate young (PI. 

 44, fig. i). Each swarmer possessed a nucleus and sev- 

 eral contractile vacuoles, while in the forward end it was 

 provided with two whips. About half an hour after leav- 

 ing the parent, it settled perpendicularly upon an object, 

 took on a spherical form and a naked Clathrulina re- 

 sulted. The stem had its origin in a depression of the 

 body which is visible on the surface as a sharply defined 

 circle (seen in PI. 44, fig. 2, in the center of the draw- 

 ing). It grows long, as represented in fig. 3, which is a 

 naked Clathrulina before the shell is formed. 



SARCODINA. RADIOLARIA. 



We may turn with a feeling of assurance to the primi- 

 tive forms of Radiolaria discovered by M. L. Cayeux 2 in 

 pre-Cambrian rocks as the remote ancestral forms of 

 Radiolaria living to-day. These minute, silicious shells 

 remained practically unchanged during the metamorphism 

 of the surrounding rock. The primitive Radiolaria were 

 spherical, spineless, and some had an imperfectly trellised 

 skeleton. Of those that were symmetrical Cenosphoera 

 (PI. 45, fig. i, x 1350; fig. 2, section of the same) was 

 one of the most generalized. The characteristic network 

 is seen in these shells with perfect clearness. Though 

 found in pre-Cambrian and Silurian rocks, this genus 

 occurs at the present time both on the surface and at 



1 See Arch. f. mikr. Anat., X, Supplement, 1874, p. 2. 



2 Bull. Soc. Geol. de France, 36 Sen, XXII, 1894, p. 197. 

 Compte Rendu Soc. Geol. de France, May, 1894, p. Ixxix. See also 

 Amer. Geol., XV, 1895, p. 146. 



