H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 329 



with the same process in Heteromtta fusiformis, Jas.-Clk., Astasia tricopkora, Clap. (§ 12), and 

 Oryntomonas (C. nov. sp.J, 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 (fig. 63) of the branches 

 are flat, and have a distinct longitudinal, irregular striation ; to all appearances made up of 

 the older, laterally agglutinated twigs. The youngest, terminal portions (fig. 47, pel) 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 (fig. 62). 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 substance 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 color, but as they taper off" into branchlets they 

 gradually assume a gamboge color, and finally terminate in scarcely colored twigs." 



" Reproduction by fissigemmation (figs. 52-61), is the only method of propagating individ- 

 uals which I have observed. As a preliminary to this process the monad gradually loses its 

 fusiform shape, and assumes at first an oval contour, and finally becomes globular (fig. 52). 

 During this transition both of the prehensile cilia (fl, fl 1 ) become much more conspicuous 

 than usual, and the body develops a closely fitting hyaline envelope (h) about it ; thus 

 passing into a sort of encysted state. The contractile vesicle (cv), however, does not seem 

 to cease its pulsations during this period, and moreover it becomes 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 oro-an 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, both the larger and 

 smaller cilium seem to be undergoing a change, and become indistinct in outline. Pres- 

 ently two larger flagella (fig. 53,/) burst upon the view, apparently by the longitudinal 

 splitting of the previously single one of the same kind, and rapidly separate from each 

 other by the broadening of the body, leaving between them the smaller cilium. The 

 latter at this time appears much thicker than usual, and seems to be composed of two 

 closely approximated, parallel threads (fl 1 ). By this time the contractile vesicle has also 

 divided into two, which lie closely side by side." 



"At this moment the time noted in one series of observations was 2.30 p. m. By 2.35 p. m. 

 (fig. 54), the larger flagella (fl) had separated still farther, and the smaller cilium had split 

 into two ( fl 1 ) very conspicuous filaments ; as yet, however, attached to a common point of 

 the body. From this time forth to the completion of the process of fissigemmation, all of the 

 cilia kept up a slow vibration, in which they undulated from base to tip with a sort of snake- 

 like motion. By 2.45 p.m. (fig. 55), the body had become quite appreciably broader than 

 lono- ; the contractile vesicles (cv) were widely separated, and the smaller cilia had left be- 

 tween them a considerable space, and each one had approximated quite near to the base of 

 a larger flagellum. At 2.50 p.m. (fig. 56), the body had become nearly twice as broad as 

 long, and the space (e 1 ) between the two pairs of cilia was nearly twice as great as in the 

 last phase, and considerably depressed in the middle, so that the body had a broadly cordate 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. Pt. 3. 7 



