120 ANATOMY AND PHYSIOLOGY 



to such an extent as to become slightly funnel-shaped, and 

 in this condition the faecal stream may be seen issuing from 

 it with considerable force. There are many other interesting 

 points in the structure of this highly organized and interest- 

 ing sponge which I will not advert to at length, but refer 

 my reader to a fuller and more complete history of its 

 stnicture published by me in the 'Transactions of the 

 Microscopical Society of London ' for 1859, vol. 7, p. 79, 

 Plate V. 



Thus we find that inhalation is the primary vital opera- 

 tion induced by cihary action, and that exhalation is merely 

 a mechanical effect arising from the primary cause. We 

 find also that these actions are separated into two distinct 

 modes ; the one exceedingly active and vigorous, exerted 

 only at intervals and for short periods, and the other gentle 

 and continuous. If we combine the consideration of these 

 peculiarities of function with those of the anatomical struc- 

 ture, we find that the incurrent streams are always received 

 in intermarginal cavities, and that these organs, however 

 modified, are always present, and in some cases can be dis- 

 tinctly and strikingly separated from the great mass of the 

 interstitial canals and cavities of the sponge. If we trace 

 the course of the inhaled fluids, we find that on their 

 entrance through the pores they are first brought into con- 

 tact with the parietes of the intermarginal cavities, and 

 passed thence into the complicated system of digestive 

 surfaces which line the incurrent and excurrent canals and 

 cavities of the sponge, and that the exhausted fluids charged 

 with faecal matters are finally discharged without the slight- 

 est return to or intermixture with the contents of the inter- 

 marginal cavities. We may therefore, it appears to me, 

 safely conclude that the respiratory and digestive functions 

 are separated, and that the latter has its seat in the inter- 

 marginal cavities, and the former in the interstitial canals 

 and cavities. 



The vital energy of the Spongiadae must be very con- 

 siderable, and the quantity of oxygen consumed by their 

 respiration great, if we may judge by the effects of their 

 presence in the vivarium, where their introduction makes 



