150 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



many persons as it has Oscula. Practically this theory leads to 

 difficulties, because some sponges have no Oscula, and because 

 similar sponges may have one, or a great many Oscula. 



To avoid this difficulty, O. Schmidt (I.e.) expounds a theory 

 according to which the sponges are not personified at all, but are 

 " Zoa impersonalia," or unlimited animals. 



Embryology. 



The Histology of sponges, as also their Embryology, was not 

 correctly described before Schulze published his observations on 

 that subject. 



Metschnikoff (152) disputes the correctness of Haeckel's obser- 

 vations on the Gastrula of Sycandra raphanus and states, that the 

 skeletophorous outer side of the sponge is formed out of the round 

 non-ciliated cells which form a plug in the Blastula. 



O. Schmidt (153) confirms the observations of Metschnikoff 

 (I.e.), and states that in other cases, besides Sycandra, no epibolic 

 Gastrula is formed. 



Also Carter (154) confirms Metschnikoff' s statements. 



In 1877, S. Kent (156) published an account of the development 

 of sponges which differs very much from the descriptions given 

 previously by F. E. Schulze and Metschnikoff. The swarming 

 ciliated gastrula is not a single individual but a " compound 

 ciliated gemmule." The ovum divides by continued fission into a 

 multitude of fringe cells, the fringe of which " has apparently 



(152). E. Metschnikoff. Spongiologische Untersuchungen. Z. f. w. Z. 

 Band. XXXIL, Seite, 349. 



( 153) 0. Schmidt Zur Orientierung iiber die Entivickelung der Schwamme 

 Z.f.wZ. Vol. XXV. Supplement, t?eite 127. No'hmals die Gastrula der 

 Kalkschwamme. Archiv. fiir mik. Anat. Band, XIV., Seite, 249. Das 

 Larvensta'Hum von Ascetta primordial is und A. clathrus. Arch. f. mik. 

 Anat. Hand, XIV, Seite, 249. 



(154). Carter. Development of the Marine Sponges. Ann. Mag. (Series 4), 

 V<J. XIV. p. 321, 389. 



(15G). Sav. Kent. Notes on the Embryolo :y of Sponges. Ann. Mag., 

 Vol. II., p. 139 . 



