round the Cilium of the Sponge-cell. 13 



Hiinilar to those of the ])rotoan, which in progression or in 

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

 that in it " may be observed hyaline vesicles of different siz&s 

 contracting and dilatini; themselves as in the jirotean.'' I 

 quote tlu'sc jiortions to show that this intercellular protoplasm 

 was described upwards of twenty years since. 



Another nhenomenon witnessed by Prof. James-Clark wa.s 

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

 cherrima (pi. 9. tigs. 13-21,1). 13), which he patiently watched 

 and lia.s as fully delineatea and described. To this also I 

 would direct attention, because I have tigured a group of 

 stnloniferous sponge-cells from Grantia compressa which bear 

 the aj>pearancc of having been produced in a similar way 

 (PI. II. tig. 19). 



But the variety of forms which these sponge-cells may 

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

 sidering the number I have tigured 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, 

 ])1. 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 

 sareode, 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 Hpongilla. 



It must be remembered that in all these instances the parts 

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

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

 wuth 710 fflass cover. 



