ERRATA AND ADDENDA. Xxi 



be restricted to the space between the mass of endochrome and the 

 integument ; for neither Mr. Bowerbank nor myself could detect it 

 in the internal parts of the endochrome. I at first supposed that the 

 circulation was confined to the margins ; nor did I perceive it else- 

 where until Mr. Bowerbank adjusted the microscope and showed me 

 that the motion extended over the whole surface of the endochrome. 

 The circulation being, as I have just stated, carried on between the 

 integument and the mass of endochrome, which is usually brought 

 fully into view by the observer, explains the difficulty experienced in 

 detecting the circulation, except at the margins. The motion was very 

 irregular : the fluid flowed at one time towards the extremities, and 

 at another in the opposite direction, and the intervals between these 

 changes were of uncertain duration. Streams also, though apparently 

 not separated by any partitions, flowed side by side in contrary di- 

 rections. The currents evidently consisted of an homogeneous fluid; 

 but from time to time minute granules were detached from the internal 

 mass of endochrome and carried along in the stream for short periods, 

 after -va hich they either returned to the quiescent portion or passed 

 into other currents. It seems to deserve particular notice that the 

 circulation was not interrupted at the suture. The process in Penium 

 Digitus was somewhat different from that just described. The flow 

 was continuous from the middle to the extremities, whence the re- 

 turning streams apparently poured back through the centre of the 

 mass of endochrome. I ought however to add that, as regards the 

 Penium, I witnessed the movement only in one specimen, and in that 

 but for a short period. I have subsequently succeeded now and then 

 in obtaining with the triplet some obscure indications of the existence 

 of a circulation ; but for the exhibition of it with any accuracy or 

 certainty the simple microscope seems altogether inadequate. 



I have mentioned in the Introduction many points of similarity 

 between Desmidieae and acknowledged Algae, and as every additional 

 fact illustrating the resemblance tends to confirm the opinion advo- 

 cated in this work, that the former belong to the vegetable kingdom, 

 I gladly seize this opportunity of stating that Mr. Jenner has recently 

 shown me in a species of Tyndaridea evident, though faint, longitu- 

 dinal striae, similar to those which are present in many Closteria, and 

 that Mr. Bowerbank has pointed out to me the same appearance in a 

 species of Tiresias. 



