OF THE PHYTOZOA. 165 



indebted for his researches among the simplest organisms of creation, additional 

 thanks are due for the elaborate essay on a new genus of Volvodnece, in 

 which he has most philosophically displayed the stmcture and relations of 

 that family at large. The new genus is named by him Stepliaiiosphcera, the 

 structui-al and physiological characters of which have been presented to the 

 English reader by an excellent translation of Cohn's original paper, in the 

 A. N. H. 1852, X. p. 321 et seq. Besides this account of Stephanosphcera 

 by its discoverer, none other exists ; we must accordingly make extensive use 

 of it in attempting an abridged description, — a difficult task on account of the 

 importance of almost eveiy paragraph it contains. 



The organisms to be described *' exhibit an extraordinary variety of size and 

 shape," writes Cohn ; " but they are aU essentially of similar structure, and 

 consist of eight green spherical corpuscles having their central points situated at 

 the circumference of a circle (XIX. 38), and of a large common envelope, en- 

 closing the former as a colourless vesicle, at the equator of which are ranged 

 the said eight green globules (XIX. 40-58). 



" The common envelope is boimded by a membrane whoUy devoid of struc- 

 tui-e and transparent, so that it may be overlooked if the illumination be not 

 properly modified, under which circumstances the 8 green globules appear 

 destitute of any common bond of union. But the membrane of the envelope 

 always exists ; and although very delicate and thin while young (XIX. 57-58), 

 it becomes thickened with age, and then possesses an evident breadth, albeit 

 no compound structure can be detected. The membrane of the envelope is ab- 

 solutely rigid, and never changes its shape, excepting through the ordinary 

 expansion of growth ; therefore it is not only totally devoid of contractility, 

 but is even elastic only in a slight degree. 



" In whatever dii'ection the total organism may lie during its movements, 

 the envelope always appears as a perfect, absolutely regular circle (XIX. 38, 

 39) ; thence it results most decidedly that the membrane of the envelope forms 

 a sphere which may perhaps deviate but very little from the mathematical 

 ideal. The diameter of the envelope varies between tolerably wide limits : 

 while some younger forms possess an envelope ^th of a line (0*028 mm.) in 

 diameter, most attain one of -g^j-th (0-044 mm.), and the largest are as much 

 as ^th of a line (0-055 mm.) in diameter. 



" The phgenomena in dissolution and duiing propagation prove that the 

 membrane of the envelope immediately surrounds a colourless watery fluid, 

 the refractive power of which does not dififer from that of water. The enve- 

 lope may therefore be regarded as a broad spherical cell with a delicate strac- 

 tiu-eless membrane, colouiiess and transparent like glass, containing a thin, 

 water-like, colouiiess fluid ; consequently I shall denominate it the envelope- 

 cell {Hull-zelle). 



" "WTiile the envelope-cell varies, generally speaking, only in size, and no 

 difference whatever of shape and stnicture can be detected in the different 

 individuals, the variations in the development of the eight green globes in its 

 interior are very great. In fact it is difficult to represent the multipHcity of 

 forms which here display themselves, so as to give a full and clear idea 

 of them; and our figm^es even can aff'ord but a very insufficient picture, 

 since scarcely a single individual exactly resembles another in this respect. 

 The eight green bodies in the interior of each envelope-ceU, which, for reasons 

 to be given hereafter, I shall call primordial cells, are in their simplest 

 condition globular, and stand at equal distances in a cii^cle at the largest 

 cii'cumference of the envelope-cell, so that the whole stnicture looks like a 

 hollow glass globe with a ring formed of eight green globules in its interior 

 (XIX. 38). If the circular line in which the centres of the eight primordial 



