ON THE LIFE-HISTORY OF THE FOEAMINIFERA. 129 



a second chamber of a characteristic shape, and, during the 

 greater part of its existence, a single large nucleus. 



The microspheric form (figs. 6 a and h) has a small central 

 chamber, and a number of small nuclei distributed through the 

 protoplasm. 



As in other species, the two forms differ greatly in the 

 frequency of their occurrence. Out of 1812 specimens which 

 I had examined up to January 12th, 1894, 52 were microspheric, 

 giving a proportion of megalospheric to microspheric forms of 

 about 34 to 1. The relative proportion of the two forms varies, 

 however, at different seasons. 



Among the microspheric forms I have met with several 

 young ones, which are far inferior in size and the number of 

 their chambers to the large megalospheric individuals. {Gf. 

 Figs. 6 a, 7, and 13, which are all magnified 170 times.) 



Before describing the characters of the two forms, certain 

 features common to both may be mentioned. 



The Structure of the Protoplasm in Preserved Specimens. — 

 When a live specimen of Polystomella is crushed under a cover- 

 slip, and examined under a high power, the protoplasm appears 

 as a colourless mass, containing granules, but not vacuolated. 



In sections of specimens killed with osmic vapour, or any of 

 the other reagents usually employed, the protoplasm is found 

 to present an appearance which resembles that of bread, the 

 granular solid portions forming walls and strands between 

 rounded vacuolar spaces, which communicate with one another 

 to a greater or less extent. This structure, for want of a better 

 name, may be referred to as a reticulum. 



In examining decalcified and preserved specimens as a 

 whole, it is often seen that the protoplasm of one chamber 

 protrudes into the next through the canals which connect the 

 chambers together. These protrusions are marked by the lines 

 of the reticulum. In the parts of the chambers away from the 

 connecting canals the reticular structure is obscurely seen, but 

 in the regions where such protrusions have occurred the strands 

 of the reticulum are seen to be drawn out parallel with one 



