AMONG SIMPLE SAKCODE ORGANISMS. 



431 



They want, however, the nucleus of the Diatomaceae. They are 

 simple non-nucleated masses of protoplasm invested by their 

 siliceous membrane. 



Fig. 15. . 



Myxastrum radians. 

 A, the Myxastrum in its encysted resting state. B, the homogeneous contents 

 of the cyst haye become broken up by radial cleavage into numerous conical 

 masses whose points touch one another in the centre of the sphere, and whose 

 rounded bases are visible at the periphery. C, the conical segments of B have 

 become fusiform, and each has excreted for itself a siliceous shell. The focus of 

 the microscope is here directed upon a meridional plane so as to show the radial 

 disposition of the fusiform spores. D, the free fusiform spore with its siliceous 

 shell. B, the protoplasmic contents of the spore escaping from its siliceous 

 shell. F, the homogeneous protoplasm of the spore which has entirely freed 

 itself from its siliceous shell, and assumed a spherical form. G, the same pro- 

 toplasm mass become the fuUy developed Myxastrum, with a multitude of fine 

 pseudopodia radiating in all directions from its periphery. (After Haeckel.) 



In this condition they remain for some time within the cyst, and 

 then, by the rupture of this, escape and become dispersed in the 

 surrounding water (D), Soon after this the homogeneous proto- 



