14 THE VOYAGE OF H.M.S. CHALLENGER. 



its larger distribution in the Sycon having brought about the differentiation of the 

 eododermic elements into flagellated and pavement-cells. 



All this was stated on the supposition that it is principally pavement-cells which take 

 in the nutritious particles. We have now to search into the corresponding physiological 

 statements. The question has its own literature, but the statements of Lieberkiihn, 1 

 Hseckel,* Carter, 3 Keller, 4 Metschnikofl', 5 Vosmaer, 6 and Krukenberg 7 upon the subject are 

 so very conflicting, that it must be regarded as very fortunate that science has recently 

 been enriched by the new detailed observations of an investigator conscious of these 

 contradictions. I speak of the beautifully illustrated memoir of Dr. v. Lendenfeld on 

 the AplysinidaB of the South Sea. 8 His physiological statements are the result of 

 numerous, and, as it seems, very carefully-made experiments. It is the more to be 

 regretted that v. Lendenfeld was not quite impartial in the execution of the task. I 

 do not mean to say that the experimenter was under the influence of the ideas on the 

 morphology of the Sponge upheld by the late Prof. Balfour, but I think that had 

 Dr. v. Lendenfeld begun his experiments in order to answer the question " Which cellular 

 elements in the Sponges do carry on the nutritious process?" instead of "Are these 

 elements of endodermic or ectodermic origin (loc. cit., p. 251)?" he would have come to 

 rather different conclusions. Dr. v. Lendenfeld suggests that — (l) all free surfaces of 

 the Sponge are able to take in the food — a very important observation, for it reconciles 

 in some measure the contradictory statements of former observers ; and that (2) while 

 the particles of carmine having entered the pavement-cells covering the subdermal 

 cavities do pass into amoeboid cells of the mesoderm in order to make their way from the 

 superior part of the Sponge to the zone of the flagellated chambers, and to be afterwards 

 pushed out by the flagellated cells, the flagellated cells neither retain the particles of 

 carmine taken in from the water, nor deliver them to the mesodermic cells, but throw 

 them out shortly after having imbibed them. 



Dr. v. Lendenfeld tells us further, that the particles of carmine, taken in by the 

 pavement-cells of the subdermal cavities, having been finally pushed out by the flagellated 

 cells, appear altered in their form, presenting now rounded not sharp edges as they did 

 before ; and that this is not the case with the particles taken up by the flagellated cells. 

 If now Dr. v. Lendenfeld comes to the conclusion that the flagellated cells are excretory 

 organs of the sponge, 1 find this conclusion very natural and even plausible, although 

 not quite beyond the reach of doubt, his experiments having been made with carmine and 

 not with really nutritious material. At all events, however, I agree with him that the 

 flagellated cells are not to be regarded as special organs concerned in the feeding of the 

 sponge. For against this there are objections from a, so to speak, mechanical point of view. 



1 Archivf. Anat. n. Physiol, p. 385, 1857. '- Kalkschwamme, Bd. i. p. 372. 



:i Ann. and Mini. Nat. Hist., ser. 5, vol. iv. p. 374, 187:). * Zeitschr.f. wiss. Zool, Bd. xxx. p. 570, 1878. 



5 Ibid., Bd. xxxii. p. 371, 1879. (; Voorloopig berigt, &c, p. 5. 



' Vergli ich nd-physiologisch Studien, Bel i. p. G5, 1879. 8 Zeitschr.f. iriss. Zool, Bd. xxxviii. p. 234, 18S3. 



