434 Prof. H. James- Clark on the Structure and 



from three to four times a minute. It lies near the surface, 

 about halfway between the two ends of the body, and nearly 

 midway betwixt the two extremes of its greater diameter. At 

 the completion of its diastole it has a circular outline, and ap- 

 pears like a clear colourless vesicle in the midst of the yellowish 

 tissue of the body. Upon contraction it disappears and leaves 

 no trace of its presence. The systole progresses slowly, as in 

 Anisonema {A. sulcata, Duj.?, and ^.nov. sp.), Cyclidium (C. nov. 

 sp.), and Phacus pleuronectes,J)u]., and in this respect contrasts 

 strongly with the same process in Heteromitafusiformis, Jas.-Clk., 

 Astasia tricophora, Clap., and Cryptomonas {C. nov. sp.), in which 

 the last half of the systole is very abrupt and marked. 



The stem. — In addition to what has already been said of the 

 general appearance of this part of the organism, it may be added 

 that the older and basal portions of the branches are flat, and 

 have a distinct longitudinal irregular striation, to all appear- 

 ance made up of the older, laterally agglutinated twigs. The 

 youngest, terminal portions of the branches which, under the 

 name of twigs, have been described in this paper as the imme- 

 diate supporters of the colonies of monads, are evidently tubular. 

 They appear to be as flexible as a spider's thread, and are usually 

 quite irregular in outline, and in the calibre of the canal which 

 permeates them. The wall of these tubular twigs is quite thick, 

 and is alike rough on the exterior and interior faces. The sub- 

 stance within the tubes appears homogeneous, but whether it is 

 solid or fluid could not be determined. The oldest part of the 

 stems is of a reddish-brown colour ; but as they taper off into 

 branchlets they gradually assume a gamboge-colour, and finally 

 terminate in scarcely coloured twigs. 



Reproduction by tissigemmation is the only method of propa- 

 gating individuals which I have observed. As a preliminary 

 to this process the monad gradually loses its fusiform shape, 

 assumes at first an oval contour, and finally becomes globular. 

 During this transition, both of the prehensile cilia become much 

 more conspicuous than usual, and the body developes a closely 

 fitting hyaline envelope about it, thus passing into a sort of en- 

 cysted state. The contractile vesicle, however, does not seem 

 to cease its pulsations during this period, and moreover it be- 

 comes quite conspicuous. This arises mostly from the fact that 

 the body is in a nearly quiet state, and allows the observer to 

 obtain a prolonged and undisturbed view of it. Unfortunately 

 the rate of the pulsations of this organ was not ascertained when 

 the following observations were made, because the whole time 

 was occupied in watching and drawing the various and rapidly 

 changing phases of self- division. 



After the body assumes a globular shape, as above mentioned, 



