380 Mr. H. J. Carter on the Nutritive and 



digestion is carried on by the collared cells of the ciliated 

 chambers," the above must be my reply. 



Although at one time the foreign material may be chiefly 

 taken in by the sponge-cells (spongozoa) of the ampullaceous 

 sac, and at another by the sponge-cells of the parenchyma, it 

 cannot be inferred that there are two systems of alimentation, 

 but rather that they are both the same, only that they are 

 respectively more or less used according to circumstances. 



Again, while it may be generally thought that there is no 

 direct communication between the inhalant orifices (pores) of 

 the surface and the exhalant or excretory canal-system of the 

 interior except through the ampullaceous sacs (" Wimper- 

 korbe"), facts now prove that branches of the excretory canal- 

 system may commence directly under the pores (no. 10, pi. vii. 

 fig. 5, and no. 21, pi. xxv. fig. 4, e, &c.) ; so that whatever 

 nutritious material may be in the water which thus passes 

 directly into the excretory canal, must be deflected from it to 

 arrive where the sponge-cells of the ampullaceous sac and 

 parenchyma respectively are naked — that is, uncovered by any 

 membrane which would prevent the particles of food from 

 coming into direct contact with them — indeed, where the 

 canals are formed by the sponge-cells alone, as stated by 

 Lieberkiihn (no. 7, p. 388). 



Bearing upon Nutrition is Starvation, under which, as I 

 have long since stated (no. 2, p. 309, and no. 6, pp. 32, 33), 

 the sponge-cells leave their " habitation" (that is, the skeleton) 

 and creep about the watchglass wherein the young Spongilla 

 might have been allowed to grow out from the seed-like body. 

 Lieberkiihn has recorded that the cells of Spongilla in the 

 river Spree at Berlin are amoeboid in the winter, but put 

 forth a cilium in spring (no. 5, p. 2) ; and this is confirmed 

 by Metschnikoff in Spongilla from the Dnieper in the months 

 of October and November, together with the well-known fact 

 that under " unfavourable " circumstances the retraction of 

 the cilium may take place at any time (no. 20, p. 375). 



But that the putting forth of the cilium in spring and its 

 retraction in winter, when, as Metschnikoff states, the Spon- 

 gilla had become charged with gem mules (seed-like bodies), 

 seems to show that the active life of this sponge takes place 

 during the warmer part of the year, like that of most orga- 

 nisms, when nourishment is chiefly required for the fulfilment 

 of the reproductive process ; and that the passive or amoeboid 

 state of the cells not only took place in the winter, when this 

 activity was not required, but that the cilium at all times 

 would be retracted under " unfavourable circumstances," ac- 

 cording to Metschnikoff (no. 20, p. 375), may be inferred 



