July me.-] AUXOSPORE-FOBMATIOX OF OUAETOCERAS DEB1LE. 147 



themselves around the nucleus which is situated at the center of 

 the frustulc. The single chromoplast is situated in one side 

 of the frustule, as a rule, towards the inner side of the chain- 

 curve. 



In the mean time the chromoplast gradually changes its 

 position. It moves towards the secondary valve and finally 

 limits itself in it. The greater part of the room within the 

 primary valve is free from any coloured substance, and is filled 

 with a highly refracting, glassy fluid. The nucleus with 

 granules around it remains in its former position. Hence the 

 chromoplasts in the adjoining frustules face each other. 



(Fig. 1.) 



Soon after the chromoplast has taken its position at one 

 end of the frustule, a small perforation appears at the middle of 

 the front girdle, i.e., the outer side of the chain-curve. The 

 hole is elliptical, 4-/J-X2.5 — 3/*, with the major axis parallel 

 with the girdle lines. The hole is not easily perceptible in the 

 water samples, but becomes very clear when the frustule has 

 been treated by some staining reagent. An aqueous solution 

 of aniline blue was found especially suitable for the purpose. 



In the next place, the part of the "plasma" membiane 

 just within the hole bulges out through the hole, filling the 

 process with the refracting glassy fluid. (Fig. 2 ) The process 

 gradually increases its size, rounding itself at the same time, 

 as the cell-content contracts in a manner of plasmolysis. The 

 whole cell-content is now constricted into two globular bodies, 

 one outside and the other within the frustule, with the con- 

 Striction point at the hole. Then the nucleus glides into the outer 

 globular body, and finally the chromoplast. (Fig. 3.). The 

 mother frustule is thus entirely emptied. The nucleus under- 

 goes no cytological change during its movement. 



The discharge of the cell-content from the frustulc is in 

 average completed in about three hour-. The whole discharged 

 mass assumes globular shape of 25-30/a in diameter and ad- 

 heres to the mother-frustule at the point of the perforation. 

 Soon afterwards, the globular body -wells up to a certain 

 extent and shapes itself into a compressed ellipsoid. Its major 



