74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the fact that thoy had to do with free-swimming larvae, whilst his 

 specimens were intra-ntcrino embryos. This dilibreuce again appears 

 to be due to the ditl'erenccs between the two localities ; in the Medi- 

 terranean there are no heavy tides and jiowerful currents, while in the 

 English Channel, and particularly near Koscoff, the tides are high and 

 the currents rapid, so that the young larvtc wonUl not have the faintest 

 chance of securing a safe settling-place. " The superfcetation thus 

 induced by external conditions," gives us " the key to the anomalous 

 development" which he describes. 



^^■ith regard to the zoological position of the sponges, Prof. Sollas 

 regards them as homoplastic with, but of independent origin to, the 

 Metazoa, and he illustrates his views by the accompanying diagram : — 



Metazoa 

 Parazoa (Sponges) 



Protozoa 



The gastrula of the Parazoa is essentially distinguished from that of 

 the Metazoa by the possession of collared flagellate cells by the 

 hypoblast. 



A possible mode of origin of the sponges is suggested ; starting 

 from a colony of choano-flagcllate Infusoria it is sujiposed that if 

 some of the individuals became " enjellied " at a different time to the 

 rest the colony would become differentiated into a set of cytoblastic 

 and a set of flagellate individuals ; the Proto^iwurjia hcecJceli of Savillo 

 Kent may be a stage in this process. After developing this idea 

 Prof. Sollas suggests that the Chondrosiada) should be removed from 

 the group INlyxospongia), wdiich would then contain only the genus 

 Halisarca. 



Mode of Digestion in Sponges.* — E. v. Lendenfeld returns to 

 the question whether the digestion of sponges is effected by the 

 ectoderm or endoderm. In an account of the Australian Ajdysinidce 

 he concluded that the digestive function was centralized in the upper 

 wall of the subdermal cavities, and that, where these are absent, it was 

 effected by the epithelia of the introductory canal system ; as this 

 region appeared from Schulze's researches to be of ectodermal origin, 

 Lendenfeld came to the conclusion that sponges absorbed their 

 nourishment by means of the ectoderm. 



He now^ points out that, if Marshall's observations on Bemera are 

 correct, the premiss that the lining of the canals is ectodermal is 

 wrong, and that, therefore, his conclusion is wrong also. He directs 

 attention again to his observation that the nourishment is absorbed in 

 the canals and not in the ciliated chambers, as taught by Carter ; the 

 intracellular digestion is probably effected by the amoeboid wandering 

 cells, while only the epithelial cells have the function of transmitting 

 the nourishing material to them. Von Lendenfeld agrees with 

 Polejaeff in thinking it not improbable that both ectodermal and 



* Proc. Liuu. Soc. N. S. Wales, ix. (1884) pp. 434-8. 



