290 PROCEEDINGS OF SOCIETIES. 



those above and below. In the triangular forms the contained 

 Staurastrum mostly stood with its angles directed towards the 

 angles of the former, with usually but a little space between the 

 ends of the Staurastrum at either end and the inner surface. 

 Not unfrequently, however, this regular position seemed to be 

 disturbed, and this especially in those outer cells of an indefinite 

 figure. When first taken the contained Staurastra seemed to 

 present their ordinary green appearance, but in many of the forms 

 shown this evening they had become more or less brown and dead- 

 looking. One distinct entity thus right in the middle of another, 

 in fact completely invested thereby, and seeming both of vegetable 

 nature, presented a somewhat startling appearance, nor, unfortu- 

 nately, could as yet any light be thrown on the mystery as to 

 how this phenomenon took place. It is worthy of note that the 

 gathering abounded with multitudes of this species of Stauras- 

 trum, with many instances of conjugation, showing the charac- 

 teristic zygospore of this, in itself, not uncommon species, though 

 not seemingly frequently to be found conjugated. It is, how- 

 ever, not very uncommon to find certain Desmidiese (especially of 

 the genus Euastrum — for instance, E. ohlongum or E. didelta) 

 completely enclosed in an elliptic or indefinitely shaped coat, 

 which is smooth, without angles or tuberculations, and with 

 colourless granular contents, the included Desmid seemingly 

 always effete and dead. Occasionally one sees more than one 

 (even three or four) enclosed in such a " cyst," or even sometimes 

 two distinct species so included. It is also to be seen in other 

 genera, such as Cosmarium and Staurastrum. Yet, though this 

 phenomenon does not seem to be very uncommon, it is not appa- 

 rently noticed in any published work. But to say that the more 

 definite and striking form now exhibited seems to be the same 

 kind of thing, is by no means an explanation. The present, in- 

 deed, differs in having a definite and marked form, the wall 

 thickened at the angles, and the contents decidedly of a green 

 colour. In fact, a priori they might be taken (at first glance, 

 and before one catches sight of the always present Staurastrum)* 

 for a distinct form of unicellular algse appertaining to Nageli's 

 genus Polyedrium. It may not be here superfluous to observe 

 that this is by no means the same thing as that adverted to 

 by Mr. Archer on a former occasion. (See Club ]\Iinutes, 

 'Microscopical Journal,' Dec, 1866.) The only assumption 

 possible in this case seems to be that they are of a parasitic 

 nature, not living simply upon the surface or inhabiting the 

 interior of the plant attacked, but surrounding and completely 

 investing it. In one instance one of these triangular produc- 

 tions contained, besides the Staurastrum, two half-joints oi Hyalo- 

 theca dissillens, thus pointing to a kind of swallowing up, so to 

 say, of the included alga> (Desmidieas) during the formation or 

 growth of these singular oi-ganisms. A question might arise. 

 Could they possibly be beings of rhizopodous nature, whose food 

 consisted of the Staurastra, and themselves passing through an 



