146 COMPARATIVE ANATOMY 



They vary from 0*4 to "04 mm. in diameter. The smaller 

 are the younger forms, and in them the large vacuoles of 

 the ectosarc form a single peripheral layer, separated by thin 

 radial walls of protoplasm. In the larger and older forms the 



Actinosphaerium Eichornii, viewed by reflected light, showing 

 the radiating pseudopodia, the lighter ectosarc, and the 

 darker central endosarc containing numerous nuclei. Two 

 contractile vacuoles are seen on the edge of the ectoplasm. 



vacuoles of the ectosarc are generally two or three layers 

 deep. 



Even in the living animal, but more easily in one which 

 has been killed with osmic acid and stained with picrocarmine, 

 one can distinguish a number of minute spherical bodies, 

 deeply stained by picrocarmine, each of which contains a more 

 darkly stained central spot. The spherical bodies are the 

 nuclei, the central spots their nucleoli. The nuclei are always 

 numerous, but more numerous in the larger and older 

 than in the smaller and younger animals. In the former 



