96 DUBLIN UNIVERSITY 



or kindred forms a study will bear with me while I try, as briefly as I 

 can, to put together a short description of the appearance, nature, and 

 position of the group to which I have, on the present occasion, the plea- 

 sure to add some new specios. 



The name " Desmidiacese" (taken from the genus Desmidium, con- 

 sidered as typical), is applied to a group of microscopic organisms, 

 undoubtedly a family of confervoid Algae, though, at first, they were asso- 

 ciated with their kindred family, the Diatomaceae, as one group, con- 

 sidered by Ehrenberg and his school as animalcules, — and, indeed, I 

 believe I would not be wrong if I stated that they were still so considered 

 by that illustrious observer. The definition of the ' ' Diatomaceae' ' is given 

 in Lindley's " Yegetable Kingdom" as follows : — "Crystalline, angular, 

 fragmentary bodies, brittle, and multiplying by spontaneous separation" — 

 and of the group so defined the Desmidiae were made a sub-order, dis- 

 tinguished from the " Diatomeae" proper, and characterized as " cylin- 

 drical." To any one at all acquainted with these two groups of organisms, 

 it appears to me that the foregoing definition will not be satisfactory. I 

 believe most modern authorities concur in the opinion that the Desmi- 

 diaceae are entitled to rank as an order of Algae, separate from but re- 

 lated to, the Diatomaceae, which latter order is thus defined by the late 

 Professor Smith : — " Plant a frustule, consisting of an unilocular or 

 imperfectly septate cell, invested with a bivalve siliceous epidermis. 

 Gemmiparous increase by self-division, during which process the cell 

 secretes a more or less siliceous connecting membrane. Eeproduction 

 by conjugation and the formation of sporangia." Various species of the 

 large group, thus accurately characterized, are met with in every ditch, 

 pond, and stream, and in the sea, some of them very common, whilst 

 others occur rarely. They are microscopic cellular organisms, free or 

 attached, occurring singly or enclosed in gelatinous tubular investments, 

 the individual frustules with yellowish or brownish contents, and pro- 

 vided with a siliceous coat, which may be broken, but not bent, and 

 composed of two usually symmetrical valves with a connecting band at 

 the suture, the siliceous coat or shell remaining permanent after the 

 organic contents have perished, and often possessing minute and elegant 

 markings. They are endowed, many of them, with a power of motion, 

 and when this was supposed to be peculiarly an animal function, it is 

 not surprising that these beautiful organisms were referred to the animal 

 kingdom. They are, however, now almost universally, and there can 



