62 



SPONGES 



Table of thk various Classes of Cells. 



I. K]>itholial stratum 



^Dermal Layer . •, II. Forooytes . - 



All. Skeletogeuous stratum 



•Gastral Layer . ^ IV. Gastral epithelium 



1. rinacooytes {rpilhelial 

 c-fh). 

 MyiH-ytes (amlradil* 



1 iYlh). 



8. Gland cells. 

 \ 4. Spoujjoblasts. 



Archaeocytcs (j>ri- 

 moniiai cdh) 



V. Amoebooytes {icamicr- 

 iiuj cells) 



VI. Tokoeytes {reprod act i if 



cflh) 



5. Pore cells. 



t>. Seleroblasts. 



7. CoUeneytes {stellate 



c.lh). 

 S. Desmacytes(_/i/>fYf«7i!s). 

 l\ Cysteneytes (bladder 



rells). 

 (10. Choanocytes {collar 



\ Cflh). 



'11. riiajjocytes {ingest iv« 



12. Troiihocytes {nutritive 



cells). 



13. Thesooytes {storage 



cells\ 



14. Statoeytcs {fjemmuh 



alls). 



1 15. Gonocytes 

 1, cells\ 



{sexual 



Historical Kevieir of Sponge HistohMpj. — The earlier observei"s by teasing 

 up sjH>ngo^ with needles sjiw amoeboid cells and sometimes ciliated cells. 

 Tlie discovery of the ivsemblance of the latter to Choanollagellata was 

 made by James-Clark (18t>7\ who, like most of his contemporaries, con- 

 sidered sponges as Trotozojui colonies. It was Leuckart ^_1854'> who tirst 

 drew attention to the architecture of the sixinge as a whole, and com- 

 j>ared it to a Coelenterate. Haeckel (^187:2'i formalised this conception, 

 and termed the two layers composing the body wall (hnual and (/«K</mi 

 respectively. His nsunes are adopted here in the s;une sense. The 

 dernial layer, which he termeii " excKierm," and compai-ed to the ectoderm 

 of Coelenterata, wi\s regiuvled by him as a syncytium, made up of fused 

 cells, the protophism of which formed the deivr ground substance of the 

 parenchyuKi, while the nuclei with a small quiuitity of protoplasm 

 formed the corpuscles. The spicules arose by crystallisation in the 

 ground substance, a condensiition of which around the spicule formed 

 its sheath. The gjistral layer ;^" entoderm ") consisted of the colljir cells, 

 fi"om which arvise the ova and s|vrmatozoj\. 



Schul/e in 1876 exposed the falsity of Haeckel's syncytium theory 

 by the discovery of the tlattened epithelium. Although this was a great 

 advance fixun the histological point of view, the conceptions of sjK)nge 

 structure which Sohulze founded upon it were less hajipy, luul in many 

 respects further from the truth, than Haeckel's views. He considered the 

 tlat epithelium to be partly ectoilerm, partly endoilerm, the collar cells 



' It is possible that the phagocytes should b« classified under the poroc>tes (see 

 aKne. p. 49, footnote). 



