MICROSCOPIC ALGiE AND FUNGI. 213 



octagonal shape, or of a quatlrate form with truncated angles ; 

 and each of the sixteen cells is enclosed in a colourless, 

 hyaline, delicate, but at the same time rigid membrane. 

 Cohn, however, has hitherto been unable to determine 

 whether this tunic contain cellulose or not. The polygonal 

 gonmm-ceWs, thus sun'ounded by a rigid membrane, are in 

 contact with each other at the angles formed by the trans- 

 parent, colourless wall, and these conjunctures have been 

 variously understood by different writers. Such as " brides 

 blanches muquenses contractiles," of Turpin, and the 

 " band-formed, tendril-like connecting tubes," of Ehrenbei'g. 

 In other respects, the gonium-spores resemble the usual 

 ' swarm-spores,' like wliich, they contain chlorophyll vesicles, 

 starch, &c. Tliey also present a variable number of spaces 

 or vacuoles, filled with water, which are sometimes so 

 numerous as to give the contents a frothy, vesicular aspect . 

 With these variable vacuoles, however, must not be con- 

 founded one, two, or three constant, sharply-defined vesicular 

 spaces, situated close to the origin of the vibratlle cilia. The 

 reproduction is effected in the usual way by the division, 

 several times repeated, of the contents of tlie cells. Into the 

 particulars of which, resulting as it does in Gouium in the 

 production of sixteen cells, Cohn enters at considerable 

 length. He then proceeds to discuss the relation of Gonium 

 to other Volvocinae, and shows, notwithstanding some dis- 

 crepancies, that it may properly be there placed. 



After this, he returns to the subject of the vacuoles in 

 the Gonium-ce\\%, and carefully distinguishes the vacuoles, 

 formed apparently by watery secretions in the protoplasma, 

 such as may be observed in all plant-cells, especially 

 when young, from others of a particular kind. In Goniiun, 

 he observed two or three vacuoles which disappeared and 

 reappeared periodically or rhythmically at short intervals — 

 and which he thence terms contractile vacuoles. He states 

 that these vacuoles are always placed near the point of 

 insertion of the vibratile cilia, and that they contract 

 alternately at regular intervals of so many seconds. Con- 

 tractile vesicles of precisely-similar kind have been observed 

 in numerous infusoria., and were even seen by Ehrenberg long 

 ago, in the zoospores of Gonium and of Volvox, who entertained 

 the extravagant notion that they were seminal vesicles. Re- 

 ferring to these facts. Dr. Cohn, however, imagines that he was 

 the first to discover the rhythmical nature of the contractions of 

 these vacuoles, and enters at very great length, and in great 

 detail, into an account of his observations. Not being aware, 

 we presume, that he was anticipated by more than a year in 



