OF CILIATED INFUSORIA 267 



shown in A, presenting the usual evenly granular condition. In B 

 we may see the first indications of the heterogenetic change visible 

 at the periphery, especially below and to the right. Such changes, 

 further advanced, are shown in C ; and further advanced still in D, 

 where the whole egg substance is evidently becoming converted 

 into a mass of hyaline vesicles, intermixed with granules and con- 

 taining granules in their interior, an appearance which is never seen 

 in Hydatina eggs undergoing their normal development. Similar 

 changes are also to be seen in other eggs represented in Fig. 75 — 

 those in A seeming to show the gradual differentiation of the 

 vesicles from the egg substance. 



The amount of granules within and between the vesicles varies 

 extremely in different specimens. Sometimes, as in Fig. 62, A 

 ( X 250), there are comparatively few in either situation. The egg 

 is then pale, and the individual vesicles being very distinct may be 

 seen to vary a good deal in size. At other times the granules in 

 both situations are much more abundant, as in B ( X 250), and it is 

 only at the periphery of the egg that the vesicles can be distinctly 

 seen. Occasionally, as development proceeds, the granules tend to 

 increase again, so as sometimes almost completely to obscure the 

 vesicular structure. Such a condition is shown in C, in which the 

 contained body was still motionless, and in the stage just preceding 

 the development of cilia. In D, on the contrary, cilia had just 

 become developed, and the embryo Ciliate was beginning to 

 revolve in a slow and almost imperceptible manner, so that a weak 

 osmic acid solution had to be run in beneath the cover-glass before 

 the photograph could be taken. No cilia are to be made out, 

 because within the egg-case — the outline of which is distinctly to 

 be seen to the left and below, as it is in C — the Ciliate is still 

 enveloped by a closely-applied hyaline membrane. 



The existence of this hyaline envelope (which, though itself 

 mostly invisible) by its presence conceals the cilia, is well shown in 

 Fig. 63 ( X 250), representing a specimen formerly revolving, which 

 was killed by a strong osmic acid solution, and then preserved in a 

 mixture of glycerine and water. It will be observed that the egg- 

 case has been broken, and that the embryo Cihate stained by the 

 osmic acid, has shrunk to a notable extent, together with its 

 hyaline envelope, so that no cilia are visible. 



Another of these embryos, found among a number of empty egg- 

 cases, was seen slowly revolving within its hyaline envelope, and is 

 shown in Fig. 64 ( X 250). The specimen represented in Fig. 65 



