round the Cilium of the Sponge-cell. 13 



similar to those of the protean, which in progression or in 

 polymorphism throws out parts of its cell in this way," and 

 that in it " may be observed hyaline vesicles of different sizes 

 contracting and dilating themselves as in the protean." I 

 quote these portions to show that this intercellular protoplasm 

 was described upwards of twenty years since. 



Another phenomenon witnessed by Prof. James-Clark was 

 the duplicative division (" fissigemmation ") of Codosiga pul- 

 cherrima (pi. 9. figs. 13-21, p. 13), which he patiently watched 

 and has as fully delineated and described. To this also I 

 would direct attention, because I have figured a group of 

 stoloniferous sponge-cells from Orantia compressa which bear 

 the appearance of having been produced in a similar way 

 (PL II. fig. 19). 



But the variety of forms which these sponge-cells may 

 assume, from their polymorphic power, is infinite ; and, con- 

 sidering the number I have figured from two or three compa- 

 ratively short examinations (Pis. I. & II. figs. 13-31) it will 

 be easily understood that to attempt to delineate all would be 

 endless. 



Another question now arises, as to how and where these 

 sponge-cells are grouped in the sponge-structure. 



Here, again, I must refer the reader to the description and 

 figure of these cells en groupe in my paper on " the Ultimate 

 Structure of Spongilla " (Annals, July 1857, vol. xx. p. 26, 

 pi. 1. fig. 5), where it will be observed that in this sponge 

 they form spherical aggregations^ each of which presents a 

 large circular transparent area (aperture?), which is capable 

 of being closed or expanded as required ; and to this aggrega- 

 tion I have given the name of " ampullaceous sac." These 

 groups are situated in the areolar cavities, which are accom- 

 panied by the excretory canal-system ; and the sponge-cells 

 of which they are composed seize the particles of food as 

 they are whirled in through the pores of the investing dermal 

 sarcode, and retain them as long as may be necessary, after 

 which the undigested parts find themselves in the excretory 

 canals. 



It is very easy to ascertain the form of the groups, because 

 the monociliated cells of which they are composed are the 

 only cells which take in the carmine or indigo, and hence their 

 shape and position are readily recognized with the microscope 

 through the semitransparent substance of the young Spongilla. 



It must be remembered that in all these instances the parts 

 were viewed in situ in the watch-glass where the young 

 Spongilla was grown, with the object-glass under water and 

 with no glass cover. 



