DESMIDIACEJE GENERAL CHARACTERS. 265 



body designated by Prof. Ehrenberg Sphcerosira volvox, is an 

 ordinary Volvox in a different phase of development. For it 

 does not present any marked feature of dissimilarity, except that 

 a large proportion of the green cells, instead of being single (as 

 in the ordinary form of Volvox) save where they are developing 

 themselves into young spheres, are very commonly double, 

 quadruple, or multiple; and the groups of ciliated cells thus 

 produced, instead of constituting a hollow sphere, form by their 

 aggregation discoid bodies, of which the separate fusiform cells 

 are connected at one end, whilst at the other they are free, each 

 being furnished with a single cilium. These clusters separate 

 themselves from the primary sphere, and swim forth freely, 

 under the forms which have been designated as Uvella and 

 Syncrypta by Prof. Ehrenberg. The further history of these 

 has not been traced ; and it does not seem improbable that more 

 than one intermediate stage may be passed through, before a 

 return is made to the type of Volvox globator? 



163. Desmidiacece. Among the simplest tribes of Protophytes, 

 there are two which are of such peculiar interest to the Micro- 

 scopist, as to need a special notice ; these are the Desmidiece (or 

 more properly Desmidiacece), and the Diatomacece. Both of them 

 have been ranked by Ehrenberg, and by many other Naturalists, 

 as Animalcules ; but the fuller knowledge of their life-history, 

 and the more extended acquaintance with the parallel histories 

 of other simple forms of Vegetation, which have been gained 

 during the last ten years, can scarcely be considered by judges 

 who are at once competent and unprejudiced, as otherwise than 

 decisive in regard to their vegetable nature. The Desmidiacece 

 are minute plants of a green color, growing in fresh water; 



fenerally speaking, the cells are independent of each other (Figs. 

 1, 75, 76) ; but sometimes those which have been formed by 

 duplicative subdivision from a single primordial cell, remain 

 adherent one to another in linear series, so as to form a filament 

 (Fig. 77) ; whilst in other instances, they constitute beautiful 

 star-like groups (Figs. 73, 74). This tribe is distinguished by 

 two peculiar features ; one of these being the semblance of a 

 subdivision into two symmetrical halves, which is seen in the 

 cells of most species, and which is sometimes so decided as to 

 have led to the belief that the cell is really doable (Fig. 75 A), 



1 The doctrine of the vegetable nature of the Volvox, which had been suggested by 

 Siebold, Braun, and other German Naturalists, was first distinctly enunciated by Prof. 

 Williamson, on the basis of the history of its development, in the "Transactions of the 

 Philosophical Society of Manchester,'' vol. ix. Subsequently Mr. G. Busk, whilst ad- 

 ducing additional evidence of the Vegetable nature of Volvox. in his extremely valuable 

 Memoir in the "Transactions of the Microscopical Society," 2d Series, vol. i, called in 

 question some of the views of Prof. Williamson, which were justified by that gentle- 

 man in his " Further Elucidations" in the same Transactions. The Author has endea- 

 vored to state the facts in which both these excellent observers agree (and which he 

 has himself had the opportunity of verifying), with the interpretation that seems to him 

 most accordant with the phenomena presented by other Protophytes; and he believes 

 that this interpretation harmonizes with what is most essential in the doctrines of both, 

 their differences having been to a certain degree reconciled by their mutual admissions. 



