GENERA, SPECIES, &C. Spong, 7 
transitional forms, and so are all Tetracladina which manifest diminution 
in the number of spicular axes. 
An adult Sponge is neither an individual nor a colony (‘‘ Stock ”), but 
an organic mass which becomes differentiated into organs. 
Discodermia^ (8) p. 22. 
Corallistes clavatella, Schmidt, (8) p. 24, pi. iii. figs. 2, 3, 5, t=- Disco- 
dermia^ixomGxxM of Mexico, connects the Tetracladina and Rhizomorina : 
var. nodosa, 1. c. p. 25, pi. iii. fig. 1 w-o, distinguished. 
Liodermatium ramosum, Schmidt, (8) p. 28, pi. i. fig. 8, = Siphonidium, 
g. n., Sombrero, 240 fath., Morro Light, 212 fath. 
Spongilla, (7) p. 375, has no collar-cells in winter ; but then and at 
some other times temporarily contracts into a solid mass. S. lacnstris 
and yiuviatilis, 1. c. p. 373 ; digestion observed to take place in mesoderm. 
Spongilla fluviatilis, Rep. E. Kent Soc. xx. pp. 26 & 42, growth observed 
under microscope on glass cell ; origin from ovaries and physiology of the 
young Sponge given by Full agar. 
Spongilla fluviatilis^ Ganin (4). From the account of this work given 
in Zool. JB. Naples, i. p. 211, the embryonal and later development 
of Spongilla fluviatilis is described as commencing with a total and 
equal segmentation, forming solid morula, which acquires an internal 
cavity whose lining cells become the endoderm, while the other cells of 
the primitive central layer form the mesoderm, the primitive outer layer 
forming the ciliated ectoderm. The mesoderm-cells aggregate especially 
at the hinder pole and give the gastric cavity its hemispherical shape ; the 
mesoderm early developes spicula ; a space between the ectoderm and 
mesoderm appears to the author to represent a body cavity. The larva 
becomes fixed by its posterior endoderm- cells, and becomes flattened out. 
The mesoderm-cells almost fill up the gastric cavity by their dispropor- 
tionate growth \ the cavity however persists and forms the ciliated 
chambers by evagination. The mouth opening is formed by a cleft 
made through the mesoderm and endoderm on the upper wall of the 
gastric cavity, and it thus opens only into the body cavity, not to the 
exterior, from which it is shut off by the ectoderm. Pores are then 
formed between the ectodermal cells and connect the mouth opening with 
the exterior ; it is thus homologous with a dermal pore. In the adult the 
ectoderm forms two layers, the mesoderm has differentiated a thin 
hyaline ground-substance ; the endoderm forms a unilaminar epithe- 
lium, clothing the surface of the various cavities of the water canals, 
with the exception of the interior of the body cavity and of the mesodermic 
septa. From the above facts as to the distribution of the endoderm in 
Spongilla^ a Coelenterate nature is assigned to Sponges. 
Hexactinellida. 
Hexactinellidce, A. K. Zittel, Beitrage zur Systematik der Fossilen 
Spongien (Stuttgart : 1879), reprinted fronl JB. f. Mineral, [c/. under 
Fossil StONGES]. Principles of proper classification set forth ; the 
skeleton spicules are a safer guide than the flesh spicules. Modifications 
of canal system described : they include a canal system proper and an 
inter-canal system. The author considers that the entire organization of 
