ORIGIN OF CILIATED INFUSORIA 231 



infusions made from living grasses just as certainly as in those 

 made from dead grasses. 



The Ciliated Infusoria which, so far as my observations go, have 

 been met with in hay infusions, and, with few exceptions, in the 

 other vegetal infusions with which I have experimented, have all 

 been species of Kolpoda. The specimens vary, however, much in 

 size, not only in different infusions, but also, to a lesser extent, in 

 the same kind of infusion. Some of the largest matrices from 

 which these Ciliates issue are to be met with in hay infusions, 

 where I have often seen them as much as 1/350 inch in diameter. 

 One of these bodies is shown in Fig. 48, A ( x 375). On the other 

 hand, about the smallest Kolpodas I have ever found have been 

 encountered in an infusion prepared from Yellow Bed Straw 

 {Galium verum), where many of them have not been more than 

 1/2000 inch in diameter. They have been small also in infusions 

 made from Dutch Clover {Trifolium repens), though not nearly so 

 small as in the previously-named infusion. Notwithstanding this 

 great variation in size, the Kolpodae are in other respects very 

 similar ; being fairly rotund, somewhat reniform in shape, and 

 covered with short cilia, as in Fig. 48, C ( X 375). Each organism 

 has a single, large, spherical nucleus (not easily visible without the 

 aid of stains), and a much more obvious large, contractile vesicle 

 at its posterior extremity. 



These Ciliates make their first recognisable appearance in the 

 substance of the pellicle, in considerable numbers, usually some- 

 where between the fourth and the eighth day. They appear as 

 spherical encysted masses, having the appearance in their primaiy 

 stage of being mere individualised portions of the substance of the 

 pellicle itself, bounded by a very delicate limiting membrane. 

 Such bodies I shall continue to speak of as Ciliate ' matrices.' The 

 contents of each gradually becomes converted into an embryo, 

 which may be seen rotating within the limiting membrane — by 

 this time slightly thicker and constituting a cyst, though still very 

 thin. The embryo may perhaps undergo fission once, twice, or 

 rarely even thrice before the individual organism, or the products 

 of fission, are enabled to free themselves from the enclosing cyst, 

 and appear as active, free-swimming organisms (Fig. 48, B, x 375). 



What may be made out as to their formation and ultimate com- 

 position is illustrated in part by Fig. 46, in which the different 

 specimens represented have been obtained, somewhere between the 

 third and the fifth days, from the pelhcles on diff§r§n| ijif usipns. Iii 



