490 E. A. MINCHIN. 
sponges living in the aquarium, and also in freshly preserved 
sponges which are contracted. 
Fig. 14 represents a section taken at random from a series 
through the piece represented in fig. 5. Here the contrac- 
tion has reached almost its limit. The spicules form in places 
as many as five layers (in the section figured the razor has dis- 
placed them a little, in a direction passing from the north to 
the south of the drawing), and the endodermic layer is now so 
thickened that the lumen of the tubes is reduced to series of 
narrow lacune. In some places the tube is even solid, as 
Oscar Schmidt described originally. It is evident from Oscar 
Schmidt’s figure of the sponge that he had to do with a very 
contracted specimen. In almost every respect the sponge 
agrees with Haeckel’s Ascetta clathrina, both in external 
form and in anatomy. It is true that the compartments 
(Facher) are not separated from one another by ‘ exoderm ” 
(i. e. mesoderm), covered on both sides with endoderm ; but if 
a specimen with folded endoderm, as in fig. 15 6, were to com- 
pletely contract, that might be the case. It is true also that 
the compartments do not contain embryos, but that, I suppose, 
would depend on the time of year at which the sponge was 
observed. 
Thus, to recapitulate: Haeckel’s Ascetta labyrinthus is 
the ordinary expanded condition of this sponge, but with 
closed oscula, like the piece shown in fig. 3. His Ascetta 
mcandrina is the same a little contracted, as in fig. 15. 
Ascetta clathrina is the sponge in an extreme state of 
contraction, as in figs.5 and 14. Finally, Ascetta mirabilis 
is this sponge partly expanded, partly contracted. 
In the walls of the tubes also there are no elements to which 
the contraction could be due except the ectoderm-cells ; and 
to the great power of contractility I attribute the fact that 
the ectoderm! in this sponge is, as Metschnikoff observed, so 
1 Mr. Bidder has recently described (loc. cit., p. 628) the ectoderm of this 
sponge as consisting of the mushroom-shaped cells described by Metschnikoff 
in the Olynthus (Clistolynthus !) form of Ascetta blanea. Ido not wish 
at present to enter into histological details, which I hope to do in another 
