ARCHER ON CONJUGATION IN SPIROTJENIA. 151 



ways hexagonal ; they are, indeed, more or less irregular, being three-, 

 four-, five-, or six-sided. 



Thus, the conjugated state of this most marked species presents two 

 noteworthy characteristics — one the doubly formed, as it were twin, 

 zygospores; the other the remarkable "honeycomb" structure ex- 

 ternally decorating them. The doubly formed or twin zygospores have 

 their parallel in a very few instances only, such as Closterium lineatum 

 (Ehr.), and Closterium Elirenhergii (Menegh.). In these the conjuga- 

 tion of the parent pair of cells gives rise to two spores, not one only, 

 as in by far the overwhelming majority of instances. But, though so 

 far agreeing with the species mentioned, there are differences of detail, 

 as is seen, proper to the species now in question. 



In the second circumstance, the " honeycomb" structure, this zygo- 

 spore is, so far as I know, absolutely unique. 



Indeed, these zygospores could not possibly in themselves be mis- 

 taken for any other unicellular algal form that I know of, if examined 

 with the requisite degree of attention. Yiewed under a moderate 

 power, there is just a possibility of the curious " asteridium" recorded 

 by me, appertaining to Penium digitus* being confounded with it (Fig. 

 4). The densely arranged short, linear spines of that structure form 

 to the eye a kind of border, which momentarily might be thought to 

 resemble the border produced by the honeycomb structure on the 

 zygospores of Spirotcenia condensata ; and the bodies themselves are, 

 moreover, much about the same size. The prevalent occurrence in 

 pairs, too, of the former, after the original wall of the Penium has dis- 

 appeared, might help to lend them a further resemblance. But I need 

 hardly insist on their wide distinctions when carefully viewed ; yet it 

 is, perhaps, not quite out of place to draw attention to these very dif- 

 ferent structures simultaneously. 



As regards the second species of Spirotsenia which it has been my 

 good fortune to find conjugated, Spirotcenia truncata (mihi),f I regret 

 that I cannot give any account of the early stages of the process. I 

 am only in a position to offer a figure of the fully-formed zygospore. 

 Here, as in by far the most of the Desmidieae, there is one spore only 

 formed. It is, however, of a novel form, so much so as that I feel 

 satisfied it could not be mistaken for that of any other species whatever 

 yet known, nor for any other described unicellular algal structure. 

 The zygospore here is equally lobate, the lobes or projections being of a 

 triangular or conical outline, the apices subacute ; there are no spines ; 

 the tint of the cell-membrane appears to be of a kind of straw colour, 

 and the contents seem to form a globose mass in the centre, leaving 

 the angular lobes void. The four empty halves of the pair of parent- 

 cells seem to remain loosely appended, each pair diametrically opposite 

 to the other, the zygospore between (Fig. 12). 



* Ante., p. 144. 



f "Proceedings of the Natural History Society of Dublin." vol. iii., p. 88, PI. II., 

 Figs. 29-31; also " Quarterly Journal of Microscopical Science," N.S.. vol.ii., PI. XII., 

 Figs. 29-31.. 



