154 NATURAL HISTOKY SOCIETY OF DUBLIN. 



quently appear to be elongated in a direction toward the poles, and very 

 often to a greater extent in one hemisphere than in the other — reaching 

 sometimes almost to the pole in one, and leaving the other partially 

 empty — that is an equatorial line in such cases would not cut the primor- 

 dial cells into equal halves. These, whose general form in this condition 

 in an old family, when viewed equatorially, may be said to be usually 

 broadly fusiform or subelliptic, frequently present several filiform, often 

 dichotomously ramified, more or less attenuated, colourless prolongations 

 of the protoplasm, especially from their opposite ends, sometimes even 

 tuft-like ; these are occasionally very divergent laterally, oreven project to- 

 wards the centre of the envelope-cell. When the organism is quite mature, 

 these colourless prolongations are mostly attached to the inner surface of 

 the envelope, but never perforate it. When a Stephanosphsera-globe 

 is seen in polar view, the outline of the primordial cells mostly appears 

 somewhat acuminate towards the common envelope, and from such apex 

 the pair of cilia take their origin. The primordial cells possess, im- 

 mersed in their substance near the middle, two symmetrically disposed 

 round bodies — called by Cohn nucleus-like vesicles, and said to possess 

 an internal cavity.* To me, indeed, they appeared quite identical with 

 the so-called " chlorophyll- vesicles" (Nag.) of other plants, to which 

 indeed Cohn afterwards compares them.f Such may convey an idea of 

 a perfect family — of a fully-grown Stephanosphaera. 



Now, as to the developmental changes connected with propagation, 

 the primordial cells, as described by Cohn, undergo three kind of changes. 

 I shall first allude to that of " macrospores." The colourless pro- 

 longations of the primordial cells become drawn in, and the primor- 

 dial cells themselves become rounded. A slight elongation of a 

 primordial cell about to vegetate then takes place; it becomes gra- 

 dually transversely constricted, and divided into two cells, which 

 expand slightly from left to right; these two cells become divided 

 each into two, those again into two, thus producing eight; the con- 

 strictions, however, taking place only in such directions that the 

 young resultant group presents the form of a flattened spheroid, 

 having somewhat the appearance, when either of the larger surfaces is 

 towards the observer, of a wheel. These changes do not take place si- 

 multaneously in all the eight primordial cells of an old sphere, but are 

 to be met with in different degrees of advancement. The further growth 

 consists in the development of a delicate common membrane closely 

 investing the young disk-like family, and in the centrifugal separa- 

 tion of the new primordial cells upon the completion of the several radial 

 constrictions, and in the development of cilia. After escape into the 

 water by the bursting of the original envelope-cell, the new envelope- 

 cell of the young family, from beirjg at first of a very considerably de- 



* Loc. cit. (" Ueber eine neue Gattung aus tier Familie der Volvocinen"), p. 83. 

 f Ibid., p. 97. 



