PORIFERA. 123 



researches of Metsclmikoff (No. 134) on this head shew that the nutriment 

 is largely earned into the mesoblast cells, which in Sycanclra appear to 

 be derived 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 chambeivs. 



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 de quelques Sponges de la Manche." Annales des. 

 Sc. Nut. Zool., vi. ser., Vol. in. 1876. 



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

 Hist., 4th series, Vol. xiv. 1874. 



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

 Vol. i. No. 9, 1878. 



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

 Functions of the Sponge." Edinburgh Phil. J., Vol. xin. and xiv., 1825, 1826. 



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



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



(128) C. Keller. Untersuchungen iiber Anatomie und Entwicklungsgescltichte 

 einiyer Spang i en. Basel, 1876. 



(1-29) C.Keller. " Studien iib. Organisation u. Entwick. d. Chalineen." Zeit. 

 f. wiss. Zool., Bd. xxvin. Ib79. 



(130) Lieberkiihn. "Beitr. z. Entwick. d. Spongillen." Miiller's Arehiv, 1856. 



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

 Arehiv, 1859. 



(132) El. Metschnikoff. "Zur Entwicklungsgeschichte der Kalkschwamme." 

 Zeit.f. wiss. Zool., Bd. xxiv. 1874. 



and Barrois' observations on the young fixed stages of Halisarca. Schulze's (No. 140) 

 observations have however proved that the flat cells lining the axial gastric chamber of 

 Sycaudraare hypoblastic in origin, and the observations of Keller (No. 129) and Ganin 

 (No. 124) have led to the same result for the flat epithelium lining part of the passages, 

 of the Silicispongiae. 



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

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



* There is a Eussian paper by the same author, containing a full account, with 

 clear illustrations, of his observations. 



