OF THE PROTOZOA. ACTINOPHRYINA. 253 



kowsky says that the nucleus of PodopTirya is ^' transverse and frequently 

 curved," and thereby implies that it is an elongated body. The nucleus of 

 Actinojphrgs oculata (says Stein, p. 159) may be brought into view either by 

 crushing the animalcule, or, much more satisfactorily, by adding dilute acetic 

 acid (XXIII. 24 h, 25 g). On viemng it from above, it appears like a round 

 hyaline cell, containing a granular nuclear mass in its centre, and suiTounded 

 by a rather condensed layer of the medullary matter. On its entire detachment, 

 by means of the acid, it is seen to possess a distinct wall, ha^i^ng a double out- 

 line ; its nucleolus, on the contrary, seems undefined and irregular in shape, 

 composed of a mere heap of fine granules. The relative size of the nucleus 

 to the whole animal is veiy considerable. Thus, whilst the majority of spe- 

 cimens had a diameter of 1-38 to 1-35'", the nucleus measured 1-125'", and 

 its nucleolus 1-250'". From his account of Act. EicJiomii, Stein would appear 

 to have seen a similar nucleus in that species ; for he states that the round 

 nucleus appeared hke a nucleus-holding cell, having a double contoui' and 

 clearly-defined waU, and containing a large, finely-granular nucleolus. 



Encysting and Repeoductive Processes of Actinophryina : — Encysting — • 

 Fission — Gemmation — Embryos — Conjugation. — Stein represents his Acti- 

 nophrys Sol and Podophrya fixa as having a double integument (XXIII. 1, 3), 

 through which the tentacles penetrate, — whilst, as we have seen, other ob- 

 servers insist upon the naked state of the muco-gelatinous body of those as 

 well as of the other species of Actinophryina. The questions therefore arise, 

 whether the being so named and described by Stein is identical with that in- 

 tended by other naturalists, and, if so, whether it is not, in the so-called 

 encysted condition, at least in its earlier stage. For Stein subsequently 

 describes and figures truly encysted examples, in which the cyst appears like 

 a plicated loose sac around the contracted body, and the tentacles in part or 

 wholly gone (XYIII. 3). Cienkowski afiirms (0^3. cit. p. 101) that the being 

 described as Actinophrys by Ehrenberg is really a non-pedunculate Acineta ; 

 and he further remarks that, although numerous points of relation exist 

 between certain ^cme^a -forms and Poclophrya flxa,h.e is unable to determine 

 whether they should be regarded as identical, or as the extreme links in the 

 morphological cycle of one and the same species. The same critical observer 

 details the process of encysting of PoclopJirya, — a process, by the way, which 

 he has not met with in ^t-me^^-form organisms having a general resemblance 

 with it. To quote his account {op. cit. p. 99), " If PodoplirycB are allowed 

 to remain several days upon the object-glass, and care is taken not to let the 

 water diy up, eveiy stage towards the quiescent condition — that is to say, 

 towards the ' encysting ' — may be followed (XXIII. 34, 36, 37). 



*' In Podophi^y a ihi^ process takes place in the following manner: — On the 

 surface of the body a gelatinous mucous layer appears to be secreted, through 

 which the tentacles pass. The tentacles disappear in the neighbourhood of 

 the peduncle ; and the gelatinous layer in this situation hardens into a loose 

 transversely-plicated membrane, whilst at the upper end it is still soft, and 

 the^ tentacles clearly visible. Ultimately these also are retracted, and the 

 entire body of the Podophrya is enveloped in a wide loose membrane ; the 

 plications are caused by parallel annular constrictions, placed at equal di- 

 stances apart, and separated 'by circular, angular, or rounded ridges ; these pli- 

 cations are in a plane perpendicular to the peduncle. At the summit of the 

 Podophrya, and often also at the base, the membrane presents deep depres- 

 sions ; the inclosed body of the Podophrya acquires on its surface a sharply- 

 defined smooth membrane, whilst the contents of the body become somewhat 

 opaque, enclosing a round clear space. The Podophrya-ajst thus formed is 

 supported by a peduncle, which is widened at the base. In many instances 



