QUARTERLY CHRONICLE OF MICROSCOPICAL 

 SCIENCE. 



MICRO-ZOOLOGY AND EMBRYOLOGY. 



Sponges. — The discussion concerning the affinities of 

 sponges, wliich Avas started by Professor HaeckePs investi- 

 gations of the calcareous group of that class of organisms and 

 by his demonstration of their many points of contact with 

 the Coelenterata, has now reached a farther stage. On the 

 one hand, Haeckel and Eimer have adduced fresh evidence 

 for the association of the sponges with the Coelenterata, whilst, 

 on the other hand, James Clark, encouraged by the confirma- 

 tory abservations of Carter, has endeavoured to strengthen 

 his assimilation of the former to compound flagellate infusoria. 



In a paper entitled '^ The American Spongilla, a Craspe- 

 date 'Flagellate Infusorian," in the 'American Journal of 

 Science and Arts,' Dec, 1871, Professor Clark describes the 

 structure of young specimens of a Spongilla, which he terms 

 Spongilla arachnoidca. He recognises a circulatory chamber 

 or series of cavities (in place of the branched canals ordi- 

 narily observed in Spongilla) into Avhich open large efferent 

 (one only in the smallest specimens) and smaller afferent 

 ostioles. The tissue of the walls of this chamber is composed 

 of a structureless cytoblastema, to which the contractility of 

 the Spongilla is ascribed. In it are scattered numerous oval 

 or round nucleated cells. The tissue thus formed is sup- 

 ported by spiculse, which raise up portions of it so as to form 

 the cavity of the circulatory chamber, the roof of the chamber 

 perforated by ostioles lianging from the spiculse like the 

 canvas of a tent from its poles. The floor presents nume- 

 rous openings which lead into small spherical cavities, the 

 " ampullaceous sacs" of Carter, densely lined with ciliated 

 monads. Professor Clark does not regard these ciliated 

 monads as performing a general circulatory function. He 

 considers that the contractility of the walls of the large 

 chamber, and that of the efferent ostioles, is sufficient to carry 

 on that process. The ciliated monads, in their nearly 

 closed sacs, are said to be the " heads" of the sponge, which 

 is a polycephalic organism, the ciliary movement of their 

 ilagella serves only to bring the water carrying food from the 

 general cavity to them. The monads are stated to possess a 

 ' collar,' such as the author described in Leucosolenia, and in 

 certain free monads ; but — why is not very clear — they are 

 distinctly declared not to be cells. It is on the strength of 



