GENERA, SPECIES, &C. 
Spong. 9 
appears, indicating the differentiation here of distinct large-nucleated 
cells, the ectoderm ; the remainder of ~the coenoblast has the appearance 
of a syncytium, and is interpreted as constituting the mesoderm. The 
mouth opening is caused by a bursting outwards of the mesoderm. The 
primitive cavity now pushes out radially, into its walls, four to six hemi- 
spherical diverticula, forming a Ccelenterate-like stage, which Marshall 
names Protactinia , in recognition of the significance which he attaches 
to it ; similar diverticula then appear on the inner surface of the whole 
upper sido, and are constrictod off until they are loft connected by but 
narrow passages with the body-cavity ; they then become connected with 
the exterior by the evagination from them of narrow canals, several of 
which unite with each other ; the common channel thus formed opens on 
the surface by a pore formed by the extrusion of a plug of mesoderm ; 
the whole gastrovascular system is lined by entoderm. This layer be- 
comes differentiated from cylindrical into flat polyhedric cells in the 
passages, and into ciliated cells in the diverticula, which thus become 
the ciliated chambers. The latter become round instead of hemispheri- 
cal, lose their original racemose arrangement, and become isolated. 
The spicules appear at first scattered in the coenoblast of the anterior 
end of the free-swimming larvae as fine siliceous tubes, enclosing soft 
axes, and always in the neighbourhood of nuclei, although no direct con- 
nection with cells was made out ; the differentiation of the form and the 
regular arrangement of the spicules first appear at the completion of the 
canal system, and are stated to result from the organized circulation of 
water through the sponge. Marshall compares the early history of the 
coenoblast with that of the segmentation cavity in Eucope. He is inclined 
to regard the pigment-spot as a primitive sense-organ. 
Reniera sp. Its growth and decay described by Noll, (13) p. 173. 
Specimens assume a flattened shape when growing on the glass of the 
aquarium, whereas on Corals ( Alcyonarial ) they project freely. 
Thalysias repens , Duch. & Mich., var. n., Carter ; and T. carbonaria , 
(2) pi. xi. figs. 10 & 11. 
Isodictya simulo, Bowerbank, renamed I. bowerbanlci by Norman, (1) 
p. 128. 
Amorphina sp., (17) p. 41, pi. i. fig. 26, Barents Sea. 
Amorphina panicea from Travemunde Bay; H. Lenz, Jahresbericht 
der Commission zur wissenschaftlichen Untersuchung der deutschen 
Meere in Kiel, Jahrgang viii.-xi. pt. i. p. 171. 
Halichondria panicea from W. Indies, (2) pi. xi. fig. 8. 
Tedania suctoria, Schmidt, (17) p. 42, pis. i. fig. 24, iii. figs. 83-88, 
Barents Sea. 
SrONGILLIDA5. 
Spongilla. In. Am. Micr. J. ii. [1881] p. 236, an account is given of 
the examination by I. llemsen of specimens of water from the Boston 
(U.S.) water supply, affected by a taste compared to that of cucumbers ; 
A. Hyatt, on examination of substances possessing this odour in inten- 
sity, and removed from a strainer at the point of exit, identifies them as 
S. Jluviatilis. 
