H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 317 



feet of figures 13, 15, 17, 19, 21, relate to one individual, and figures 11, 12, 14, 16, 18, 20, 

 22 to another belonging to the same colony. The rate of progress of the former when the 

 drawings were made was not noted, but that of the latter set was observed in four out 

 of six of the intervals which occurred between the phases which the figures represent, and 

 during the progressive steps of the latter it was carefully recorded which of the successive 

 stages of the former filled the intervals between those of the latter ; so that it can be said, in 

 the strictest sense, that all of the figures of both sets of observations represent the phases 

 which were distinctly marked in the second series. In this way the fullest illustration pos- 

 sible was obtained, and no point was left unexplained. The whole time occupied by the 

 process in the second series was forty minutes. It has already been mentioned, when de- 

 scribing the form of the collar, that it assumes a bulging, campanulate outline (fig. 11, b) as 

 a preparatory, preliminary act in fissigemmation. In addition to this it should be stated 

 that it widens inordinately at the distal end, so as to exceed, by one third, its normal 

 breadth ; but before it finally settles itself into this shape and proportions it contracts and 

 expands its diameter by a peculiar sort of vibrating motion, and passes through a series of 

 changes of form which vary from funnel-shape to a narrower cylindrical outline, or from 

 either of these to a broader cylindrical proportion, such for instance as figures 9 and 10 — 

 representing the same individual — exemplify. This would appear also to be the time when 

 the contractile vesicles divide, for at no other period were they observed to be more than 

 two in number, as they are represented in figures 9 and 10 (cv). 



Immediately after this preparatory sign was discovered, — the time being noted at 12.55 

 p.m., — the flagellum became unusually conspicuous, and much thicker, and moreover it 

 lost its sigmoid flexure and assumed a perfectly straight carriage, with the slightest possible 

 tremulous, vibratory motion. Within a very few minutes after this the flagellum began to 

 shorten as if retracting, — reminding one of the running down of a cotton thread in the 

 flame of a candle, — and in one minute's time it became reduced (fig. 12, fl) to a length 

 which was somewhat less than half the height of the collar (b), and then it rapidly disap- 

 peared, and left no trace of its former position. During this process the body shortened 

 and became broader (fig. 12), in the same direction that the plane of the arc of the flagellum 

 formerly trended in, and consequently the contractile vesicles (cv) were more widely sepa- 

 rated ; and, the front (fr) also having become proportionately extended laterally, the base 

 of the collar (b) was also increased in diameter until it almost equalled that of the distal 

 end, so that, as a whole, it was almost cylindrical. 



In less than fifteen minutes after the preparatory stage was observed, the collar had be- 

 come cylindrical (fig. 13,5) by a combined action of the base and distal end, which consisted 

 in a narrowing of the latter and a broadening of the former. 



It was not until 1.15 p. m. that a decided mark of incipient self-division became evident 

 in the guise of a narrow, slight furrow (fig. 14, e), which extended, medianly, from the front 

 to over half way toward the posterior end of the body. By this time the body had broad- 

 ened until it was wider than long, and the collar (b) — having followed this expansion at its 

 basal portion whilst its upper extreme had contracted a little — had assumed the form of a 

 high, truncate cone. 



In two or three minutes after this the body had become distinctly indented (fig. 15, e 1 ) at 

 the anterior termination of the furrow (fig. 15, c), and the latter had grown longer and more 

 distinct, whilst the collar (b) had approximated more closely in shape to a perfect cone. 



MEMOIES BOST. SOC. NAT. HIST. Vol. I. Pt. 3. -4 



