E. MAESIIALLI. — ARCPI.EOCVTES. 169 



the choanosome in tlie parietal ledges as well as in the general 

 sponge-wall. After the cells have increased to a certain number, 

 they no longer arrange themselves in a layer but begin to heap 

 up in solid and compact masses. At ilrst the shape of such masses 

 is rather irregular, conforming more or less to that of the inter- 

 cameral space in which tliey are situated. With continued in- 

 crease in the number of the cells and consequently in the size 

 of the mass, the latter assumes a roundish, oval or broadly 

 lobose shape, measuring up to 100," or more across. An excep- 

 tionally large mass that I met with was ol)long in shape and 

 measured 230// by 150 /i. The number of cells in such a large 

 mass must amount to tens of thousands. 



The above masses vary somewhat in their frequency in 

 different specimens ; on tlie whole, they are common in the posi- 

 tions indicated in all large individuals. On stained sections, when 

 seen under a low power, they are very conspicuous on account 

 of their being strongly colored and forming compact bodies of 

 various sizes and shapes, situated among the chambers (PI. IV, 

 fig. 28, a.cL). They appear to consist of deeply stained, uni- 

 formly small spherules, densely packed together. Under a very 

 high power of the microscope, the spherules prove to be the 

 archneocytes. The outer surface of the mass is tolerably even ; 

 the greater part of it presses apparently directly upon the walls 

 of the adjoining chambers. AVhere it is exposed to the incurrent 

 lacuna;, it seems to be covered by simply a layer of cobweb-like 

 trabeculce. A continuous follicular envelope does not exist. 



Whether all the smaller archseocyte-groups on the chamber- 

 wall in more peripheral parts of the choanosome are destined to 

 form eventually such large masses as I have just described, I do 

 not know. Probably they are. In small and young specimens 



