XVII. SP0NGI2E. 
8 Spong . 
pr^porales” correspond to our term subdermal cavities (Subder- 
malraum), and his term “ cavit^s intracorticales ” to our canals or lacunes 
of the cortex (Uindenkanale oder Lakunen). What we call pores Topsent 
terms stomions, and the canals which lead down from them to the sub- 
dermal cavities euthuchones, if they run direct, and plagiochones, if they 
pass through lacunes. 
The oscules of the Garnosa lie, according to him, on the summits 
of the lobes ( Oscarella ), or more frequently on papillae. Placinastrella 
and Chondrosia have a single raised osculum. In Placina, Placortis , and 
Corticium the oscula are not distinguished from the afferent pores, only 
perhaps a little larger. 
c. Skeleton (48, 57, 61). 
Minciiin (48) states that in Ascettci coriacea the spicules are formed by 
six cells derived from the outer epithelium. Three epithelial cells 
wander inwards, and each dividing into two give rise to these six cells. 
They form two layers of three each, the lower forms the spicule. Often 
the three rays of the spicule appear to be formed separately and afterwards 
joined in the centre. Each one of the three lower cells forms one ray, 
and afterwards continues to secrete the calcareous substance necessary for 
its growth, at first at the base. When the base has attained its full 
thickness the cell wanders outwards, thickening the ray to its full stout- 
ness as it goes, and finally, when the ray has attained its full size, it lies 
at the extreme tip of the ray. Concerning the phylogeny of Sponge spi- 
cules Minciiin upholds the views of Schulze against Dreyer. 
F. E. Schulze (57) states that in the Hexactinellids most of the 
megascleres continue to grow with the Sponge. They are much larger in 
large than in small specimens, and their dimensions cannot therefore be 
used for systematic purposes. The microscleres on the contrary, par- 
ticularly the Amphidiscs, the Pinules, and the Microhexactins of the 
Hyalonematidce do not grow secondarily, but always have nearly the same 
constant size, so that their dimensions can very well be utilized by the 
systematist for distinguishing the species. The number of these spicules 
is variable; large specimens may contain many microscleres of a par- 
ticular kind, whereas only very few or none at all are found in small 
specimens of obviously the same species. 
According to Topsent (61) no diactine megascleres occur in the 
Carnosa except in Triptolemus. He considers the microchelotrop as 
the typical spicule of Placina , Placinastrella , and Corticium , from which 
all other spicule-forms of these Sponges have been derived. Dercitus 
has chelotrop or short-shafted triaen megascleres and microrhabd 
microscleres. In Dercitus bucklandi toxes occur also. Topsent considers 
these toxes as peculiarly modified diactine asters, and states that in the 
species of Thoasa all transitions between four-, three-, and two rayed asters 
are met with ; that the rays of these asters are curved ; and that some 
of the diactine forms are very similar to toxes. 
