M. C. Mereschkowsky on a new Genus of Sponge. 73 
If this is the case, we may be sure that we have to do with a 
calcareous body ; on the contrary, when the contours gradually 
disappear and the spicules can hardly be perceived, we may 
conclude that they are siliceous. 
The following are the comparative measurements of this 
sponge :— 
millim 
Potal length of the sponge). < oxic. sok. oe als 0°5-0°8 
Diameter of the head in an adult individual .. 0-1012 
ae Me a young individual .. 0:05885 
Average thickness of the peduncle .......... 0-018 
Length of the large spicules of the head ...... 0-01175-0:05875 
Thickness (sometimes not measurable)........ 0-00047-0:00117 
Length of the small spictles... 0.0... 2.05 0-00964—0:01605* 
It remains for me to explain the reasons which have led 
me to regard this animal as a sponge. It will be noticed 
that I have said nothing about pores, and this because I have 
found it impossible to find any. In spite of all my endeavours 
I have been unable to discover, either in the individual which I 
selected to study in the living state, or in those preserved in 
alcohol, any trace of pores; but it must not be forgotten that 
even if they existed, which is more than probable, it would be 
perfectly impossible to see them through the forest of innume- 
rable spicules which cover the whole surface of the head and 
conceal its surface from the eyes of the observer. It must also 
be taken into consideration that the pores are not constant, and 
that the least irritation, especially the action of spirits of wine, 
is sufficient to close them, which would perfectly explain their 
absence. ‘The same spicules coupled with the slight transpa- 
rency of the head generally have also rendered it impossible 
for me to ascertain the existence of a buccal orifice at the 
extremity of the body, although I suppose such an orifice must 
exist from the analogy of what we see in the Physemaria. 
But even if we admit that the existence of pores in Wagne- 
rella is a fact unproved and even improbable, their absence 
cannot in any way lead us to doubt its spongiarian nature. 
In fact we are acquainted with several sponges the spicules 
of which have been described, but of which the pores, for 
different reasons, have not been discovered (see, for example, 
Bowerbank’s monograph) ; and nevertheless we no not hesi- 
tate to admit that these are true sponges. Moreover we are 
acquainted with a marvellous sponge described by G. O. 
Sars in his interesting book ‘On some remarkable Forms of 
Animal Life from the Great Deeps off the Norwegian Coast’ 
*« The latter number refers to the head. 
