150 SUMMARY. 



from the granular cells, and also that it is taken up by the cells which line 

 the passages, though not by the superficial epiblast cells. Whether the 

 collared cells generally absorb nutriment is not clear from his statements : 

 but he finds that they do not do so in SilicispongicE. 



Professor Schulze has informed me by letter that he finds the collared 

 cells to be respiratory in function, while the cells derived from the granular 

 cells in Sycandra are nutritive. Carter 1 , on the contrary, from his obser- 

 vations on Spongilla, has fully satisfied himself that the food is absorbed 

 by the cells lining the ciliated chambers. 



If it is eventually proved by further experiments on the nutrition of 

 sponges, that digestion is mainly carried on by the general cells lining the 

 passages and the mesoblast cells, and not for the most part by the ciliated 

 cells, it is clear that the epiblast, mesoblast and hypoblast of sponges will 

 not correspond with the similarly named layers in the Ccelenterata and other 

 Metazoa. The invaginated hypoblast will be the respiratory layer and 

 the epiblast and mesoblast the digestive and sensory layers ; the sensory 

 function being probably mainly localized in the epithelium on the sur- 

 face, and the digestive one in the epithelium lining the passages and in 

 the mesoblast. Such a fundamental difference in the primary function of 

 the germinal layers between the Spongida and the other Metazoa, would 

 necessarily involve the creation of a special division of the Metazoa for the 

 reception of the former group. 



BIBLIOGRAPHY. 



(122) C. Barrois. " Embryologie cle quelques eponges de la Manche." An- 

 nales des Sc. Nat. Zool., vi. ser., Vol. in. 1876. 



(123) Carter. " Development of the Marine Sponges." Annals and Mag. of 

 Nat. Hist., 4th series, Vol. xi v. 1874. 



(124) Ganin 2 . "Zur Entwicklung d. Spongilla fluviatilis." Zoologischer An- 

 zeiger. Vol. I. No. 9, 1.878. 



(125) Robert Grant. "Observations and Experiments on the Structure and 

 Functions of the Sponge." Edinburgh Phil. J., Vol. xm. and XIV., 1825, 1826. 



(126) E. Haeckel. Die Kalkscfnvamme, 1872. 



(127) E. Haeckel. Studien zur Gastraa-Theorie. Jena, 1877. 



(128) C. Keller. Untersuchungoi uber Anatomic und Entivicklungsgeschichte 

 einiger Spongien. Basel, 1876. 



(129) C. Keller. " Studien lib. Organisation u. Entwick. d. Chalineen." 

 Zeit.f. wiss. Zool., Bd. xxvni. 1879. 



(130) Lieberkiihn. " Beitr. z. Entwick. d. Spongillen." Miiller's Archiv, 

 1856. 



(131) Lieberkiihn. " Neue Beitrage zur Anatomic der Spongien." Miiller's 

 Archiv, 1859. 



1 "On the Nutritive and Reproductive Processes of Sponges." Ann. and Mag. 

 of Nat. Hist., Vol. iv. Ser. v. 1879. 



2 There is a Russian paper by the same author, containing a full account, with 

 clear illustrations, of his observations. 



