14 GENERAL HISTOEY OF THE INFUSORIA. 



The coupling of the fronds generally takes place from the convex margin, 

 but may occur on the concave, or even the convex margin of one frond may 

 couple with the concave of the other." 



The Rev. W. Smith (A. N. H. 1850) represents the conjugation of 

 Closterium Ehrenhergii to be peculiar (XYI. 11, 12, 13, 14). The fii'st 

 phenomenon (he tells us) is an alteration in the granular condition of the 

 endochrome. This, from a light yellowish green, passes to a much darker 

 shade, and the larger granules, or '' diaphanous vesicles " of Ealfs, which 

 were originally few in number, and arranged in a somewhat irregular longi- 

 tudinal series (XVI. 10), become exceedingly numerous and pervade the 

 entire frond. While this change is about taking place, the fronds approach 

 in pairs, approximating by their concave surfaces, and finally coming into 

 such close neighbourhood that their inflated centres are in contact and their 

 extremities slightly overlapped (XYI. 11). In a short time, probably in the 

 course of twenty-four hours, a remarkable change takes place, both in the 

 appearance and condition of the fronds ; a mass of delicate mucus is secreted 

 around the approximated fronds ; these remove to a little distance from each 

 other, undergo " self -division," and present altogether an irregular oval figiire, 

 the outline of which is formed by the periphery of the mucus, the four divi- 

 sions of the fronds being placed in the middle in a somewhat quadi'ilateral 

 manner (XYI. 12). Duiing the progress of cell-division, the internal mem- 

 brane of the cell-wall becomes enlarged at the suture or line of separation, 

 and projects in the form of an irregular cone, with a blunt or rounded apex 

 forming a beak, whose side view presents a triangular outhne. This beak 

 becomes fiUed with endochrome, either by the dilatation or increase of the 

 contents of the half-frond, and the divided frond assimies the appearance of 

 one with two unequal segments (12), being what M. Morren calls '' a Clos- 

 terium of two unequal cones." On these membranous expansions, at the con- 

 cave sui-faces of the fronds, and close to the original sutm-es, there appear, 

 almost simultaneously with the fonuation of the beaks, two cii'cular projec- 

 tions, which, rupturing at their apices, give egress to the delicate sacs which 

 enclose the endochrome, and which, drawing with them their contents, and 

 meeting with the endochrome sacs emitted through similar projections from 

 the other half-fronds, form, by their connexion, irregular masses, which 

 quickly consolidate and assume the appearance of perfectly circular, smooth, 

 dark-coloui'ed baUs, the sporangia of Ralfs and seminules of Morren. 



Lastly, we may add, that Siebold {J. M. S. 1853, pp. 118, 119) remarks that 

 the conjugation in Closterium Diance, C. lineatum, C. striolatum, C. setaceum, 

 &c., differs from that in C. Lunula, G. rostratum, and other members of the 

 family, by dehiscence at the central transverse suture, and the consequent 

 coalescence of the contents of the two cells into a rounded or angular mass, — 

 an observation which tallies with the account presented us by Mr. Ealfs. 



Braun (On Rejuvenescence, B. S. p. 286 et seq.), speaking of conjugation 

 generally in simple cells, gives an elaborate view of the Variations the phe- 

 nomenon exhibits, and arranges them under several heads. Thus among the 

 Desmidiese " the conjugating cells unite with participation of the external 

 membrane, [and] the reproductive cell is formed [either] through contraction 

 of the contents clothed by the internal cell-membrane, [or] out of the mere 

 contents as a new cell inside the mother- ceU." But in the majority of the 

 Desmidieae, " the conjugating cells, after dehiscence of the outer membrane, 

 unite through the inner ; the reproductive ceU is formed out of the mere 

 contents as a new cell inside the conjugation-cell." By the first-named 

 mode, " the formation of the reproductive cell is ... . not a direct result of 

 the conjugation, but it is formed subsequently in the interior of the con- 



