1900] MICROSCOPICAL JOURNAL. 331 



material are carried to every part and parcel of the body 

 by means of the circulatory system ; in the sponge, the sea 

 water courses through the canal-system, carrying not only 

 the oxygen which is necessary for the continual oxidation 

 of every part of the sponge, but also particles of nutrient 

 material which will ultimately be absorbed by the special 

 cells set apart for digestive purposes. 



And this leads us to ask for a more detailed knowledge 

 of the system concerned in the alimentation of the sponge. 

 Some of the necessary details for this knowledge can be 

 gained by recourse to a few thin sections cut transverse- 

 ly with an ordinary razor through one of the cylindrical 

 sponges. If these sections are placed in a shallow vessel 

 the central gastral cavity is at once apparent, and radiat- 

 ing from it towards the margin of the section thimble- 

 like spaces are seen, whilst between adjacent spaces is *a 

 thin texture of gelatinous material in which are embedded 

 spicules of lime of various shapes and sizes matted to- 

 gether in a definite manner to form a support to the spaces 

 lying near it. The special arrangement of the spicules, 

 like links in a suit of chain-armour, to form the skeleton, 

 allows, as we shall see afterwards, of a free course to any 

 water entering or leaving the sponge. For the present we 

 must leave the consideration of the skeleton and confine 

 our attention to the part played by the thimble-like cham- 

 bers in the very necessary duty of keeping the sponge 

 alive. Our rough sections will not furnish the necessary 

 details, but if by special methods of staining and embed- 

 ding in paraffin we are able to obtain sections the 1-1000 

 in. thick, we see at once that these chambers are lined by 

 a very specialized kind of cell, known from peculiar ap- 

 pendages it possesses as a "flagellate collared cell," and 

 giving to the chambers to which they are confined the 

 name of flagellate chambers. 



These collared cells play such an important part in the 

 economy of sponges that we must have a very clear con- 



