OF THE PROTOZOA. CILIATA. 357 



in Stem's history of ChUodon CucuUulus (op. cit. p. 134). At a preceding page 

 (p. 342) we have given an abstract of the mode of encysting of this animal, and 

 have stated that the capsule remains gelatinous and soft. Inside the cyst, 

 Stein discovered an actively- moving embryo contained within a special cavity 

 (XXIX. 54-56), occupying precisely the spot where in other encysted Chilo- 

 clons the nucleus is found, -viz. in the chagonal line connecting the two oppo- 

 site contractile spaces. The embryo had an oval or ovate compressed figure, 

 with one side straight or gently curved, and the anterior extremity notched. 

 Its entire surface was covered with longitudinal, widely-separated rows of 

 unusually long cilia, in incessant motion, which tiu^ned it in a spii'al or vermi- 

 cular manner. Pressiu-e on the cyst caused its expulsion (XXIX. 59), either 

 alone or together with the substance of the parent- cyst, to which it always 

 remained adherent. This embryo. Stein concludes, is derived from the nucleus. 

 Many cysts may be met with in which the nucleus is replaced by a much 

 larger body, having a different consistence, opaque and motionless, and 

 possessing in all respects the outhne of a germ. On pressing it out of its 

 place, its siu'face is seen to be not quite naked, but to have short, stiff, and 

 imperfectly-developed cilia at one end or entirely around its margin. 



Since the embryo occupies the site of the nucleus, it might at first sight 

 be supposed that the latter was wholly transformed into it; but analogy 

 leads us to the contrary inference, that the nucleus, although obscm^ed from 

 view by the internal germ, is nevertheless present ; and this conclusion is 

 fuiiher supported by the fact, that a successive development of embi^os goes 

 on until the entire contents of the cyst are used up in their formation, an 

 event that does not occur without the influence of a nucleus. 



Stein declares the embiyo (XXIX. 59) to be precisely similar to Cydidimn 

 Glaucoma, both in figure and movements. Its size varies with that of the 

 animalcule producing it ; and individuals of aU sizes may imdergo the 

 encysting process. The smallest cysts met with were ^"' in length, and 

 their embryo not more than ^hs'" > ^^® largest y^-'", and their embryo from 

 ■^'" to ^■" (XXIX. 56). 



A remarkable circumstance happens in the case of some encysted Chilodons, 

 even after they have given birth to one or more embryos, — viz. that they 

 seem to emerge from their quiescent state and resume their active form. For 

 instance. Stein met with cysts containing a freely-moving Cliilodon, together 

 with an active embryo, both which ultimately escaped by an aperture in 

 their walls (XXIX. 58). This revi\'ification of the ciliated Chilodon as above 

 referred to, is urged by Stein as an argument to prove that the cilia are not 

 lost or destroyed when encysting takes place, but probably merely closely 

 compressed against the surface. 



Another variety of development of germs within an encysted animalcule 

 is seen in Colpoda Cuctdlus (XXIX. 35-47), which we have described under 

 the head of '' Fission," since the formation of the germs is the consequence 

 of self-divison of the whole animal either into two or, as a rule, into four 

 segments, which themselves become individually encysted, and present their 

 own nucleus and contractile space. This plan of development explains the 

 occurrence of very small encysted Colpodm. 



It was in this genus that Ehi'enberg conceived he had made out very 

 clearly the hermaphroditism and cyclical development of " Polygastrica." 



A third way in which the encysting of an animalcule is made to serve the 

 process of development is by the resolution of the nucleus into a multitude 

 of minute segments, each eventually assuming an independent animal ex- 

 istence. This formation of what may be caUed brood-cysts, occurs, as 

 shown by Stein's later researches, in Vorticella microstoma (XXIII. 10-14), 



