PORIFERA. 807 



free process, springing from a mesoglaeal cell with one or more basal outrunners, 

 near to which cells apparently ganglionic have been detected occasionally. A 

 synocil, as yet observed only in a Sycandra, is a process of mesoglaea, 'i mm. long, 

 containing a number of fine filaments derived from as many cells situate at its 

 base \ Palpocils have hitherto not been found in Calcarea Homocoela : but in 

 other sponges they occur round or near the pores of the inhalent canals (various 

 Syconidae, Vosmaera gracilis] ; on the outer surface in groups or singly (various Leu- 

 conidae] ; upon the vestibular membranes (Aulena villosd] ; upon the membranes of 

 the lacunar inhalent system (Halme globosa); or bordering the margins of the 

 lacunar extensions of the exhalent system (Euspongia canaliculataanfractuosd]. 



There is in some Non- Calcarea a marked structural difference between the super- 

 ficial and deep portions of the mesoglaea, constituting a cortex and medulla. This 

 is especially the case in Chondrostdae, where the cortex is fibrillate ; in Cortirium, 

 where it contains lacunae, each lodging a cell which fills it partially ; in Weberella, 

 Polymastia, &c., where it has a plentiful mesoglaea, imbedding stellate and fusiform 

 cells and fibrils ; in Tethyadae and Geodidae, where its structure is complex, due 

 partly to layers of peculiar spicules, of cells, of contractile fibre cells. The meso- 

 glaea round the ampullae is generally granular, but not in Spongelidae. 



The mode in which nutrition is effected has given rise to much debate. A 

 living sponge is traversed by currents of water passing in at the pores and out of 

 the oscula, or, if oscula are absent, out of other pores (see p. 793, and note i). 

 The currents may be suspended, but probably not reversed : they may be swift 

 (? nutritive) or slow (? respiratory). Nutritive substances, whether animal or vege- 

 table, alive or dead, are carried into the sponge suspended in the currents ; and 

 they have been observed in the mesoglaeal cells ; see Metschnikoff, Z. W. Z. xxxii. 

 pp. 372, 374; von Lendenfeld, Z. W. Z. xxxviii. p. 254. Particles of carmine sus- 

 pended in water are taken up solely by the collared cells in the young Spongilla 

 (Carter) and Oscarella (Heider). Metschnikoff found (loc. cit.) that in Ascetta (Leu- 

 cosolenia] primordialis and Spongilla carmine particles were taken up by the collared 

 and mesoglaeal cells ; so too in Halisarca Dujardini and H. pontica. Over- 

 feeding the latter caused obliteration of the canals. On the other hand, no 

 carmine was discoverable in the ampullae of Reniera aquaeductus and Siphono- 

 chalina cortacea, though present in the mesoglaeal cells. Von Lendenfeld experi- 

 mented on Aplysilla violacea. Carmine particles were taken up by the epithelia of 

 all parts if the sponge were kept for a sufficiently long time in water containing 

 them in suspension ; but the particles absorbed by the ectoderm of the subdermal 

 cavities soon passed into the amoeboid wandering cells which were present in 

 numbers in that part of the sponge ; by them they were conveyed to the ampullae, 

 and then excreted by the collared cells in a few days' time. Their angles were 

 rounded off. Particels absorbed by the collared cells themselves were expelled un- 

 changed. Whilst the epithelia of the subdermal cavities and ampullae, and the 

 mesoglaeal cells were thus freed from carmine, this was not the case with the 

 epithelia of other parts, even after the lapse of two months. The obvious con- 

 clusion is that absorption takes place by the ectoderm of the subdermal cavities, 

 digestion by the mesoglaeal cells, excretion by the collared cells. Polejaeff thinks 

 (Calcarea, p. 15) that a nutritive function must be assigned also to the endodermic 



1 The synocils probably shrink at death ; hence their cells may become separated. 



