OF THE PnYTOZOA. 157 



Paxdoeixa (XIX. 59-G9 ; XX. 22, 23).— This genus has recently been 

 very carefully and thoroughly examined by Prof. Henfrey {J. M. S. 1856, 

 p. 49) in an able memoir, of which we shall make free use to sujDply our 

 readers with a satisfactory description of this interesting and beautiful or- 

 ganism. The specimens examined were of the species Pandorina Morum, 

 of which, as Prof. Henfrey justly remarks, the description " given by Ehren- 

 berg is so incorrect, that no one would be able to determine the organism by 

 its aid ; but the figiu'es in the Infusionsfhierchen, although nide, are sufficient 

 for identification." Dujarchn contributed nothing to our knowledge of this 

 genus, which he treated as one with Eudorina, objecting, veiy justly, to the 

 worthlessness of the red speck as a distinctive generic character between them. 



Prof. Henfrey's account is so succinct that it admits of no abridgement, we 

 are therefore induced to present it entiiT. " The forms," he writes (p. 50, 

 op. cit.), "presented by this organism are exceedingly varied; and nothino- 

 can be more beautiful than a number of them revolving slowly on their long- 

 axes in a di'op of water, as seen under a power of about 100 diameters. In 

 the fii'st place, the perfect form exhibits two patterns (shown in XIX. figs. 

 59 and 60) ; and there are minute countei-parts to these, remaining in that 

 state, while, in the water whore the species is actively multiphdng, aU sizes 

 between fig. 64:, just emerged from the parent frond, and the full-grown form, 

 figs. 59 and 60, &c., occur. The form ^nth 32 gonidia results from the cell- 

 division going on one stage fiulher than in the form with 16 ; but this dif- 

 ference is fixed during the earhest stages of development, as the form with 

 16 never changes into that with 32 after it has become free from the parent. 

 In the perfect forms the gonidia are arranged near the peripheiy of the frond 

 in cii'cles, like the equator and parallels of latitude on a globe, — so that Pan- 

 dorina resembles Cohn's Stephanosijha'ra more closely than any of the other 

 Volvocinece, that ha\*ing a single equatorial ring of gonidia in its globular 

 frond. Among the forms with the isolated gonidia occm^ others almost equally 

 numerous with the gonidia collected together into berry-like heaps (figs. 65- 

 68) : these are smaller than the others, but equally varied in dimensions ; 

 their gonidia resemble those of the other form; they ajDpear destined to 

 form the resting-spores. 



'' The gonidia are almost globular ; they have no proper membrane, but 

 consist of a gelatinous granular substance which contains a thinner fluid in 

 the centre, as it contracts strongly by exosmosis when strong saline solutions 

 are applied. There is a large nucleus-like body (the chlorophyll-vesicle of 

 A. Braun) at the posterior end of the gonidium (fig. 61) ; and at the opposite 

 side is a short beak-like process, with a colourless space behind it : the pair 

 of cilia arise here ; and a little to one side and below these is the reddish - 

 brown granule called the ' eye-spot.' AVe have never been able to obseiwe a 

 pulsating vacuole, as described by Busk and Cohn in Volvox and Gonium. 



" The gelatinous frond appears to be perfectly homogeneous, without any 

 boundary membrane. Iodine and sulphuric acid do not coloiu' it blue. It is 

 tolerably resistent, and appears solid, as it does not give way or become 

 indented by external pressure, as is the case with the hollow frond of Vohox. 



''The fronds are multiplied by the conversion of the gonidia into new 

 families. If they are \dewed at night, many of the fronds may be found at 

 rest at the bottom of the vessel (in the daytime they assemble at the side 

 next the Hght), motionless, and Avith the gonidia rounded and deprived of 

 their nucleus. By covering up the bottle from the light, the development of 

 the new fronds, which naturally takes place very early in the morning, may 

 be retarded, so as to be followed during the morning until noon. Some of the 

 fronds may be found with the gonidia converted into berry-like heaps (fig. 62), 



