90 PROCEEDINGS OF THE 



using a binocular would find it of great service to them. The 

 President proposed a vote of thanks to Mr. Traviss for bringing 

 the model to the notice of the meeting. This was carried unani- 

 mously. 



The President then invited Vice-President D. J. Scourfield to 

 take the chair. 



Prof. Dendy said he did not intend to give a formal lecture, 

 but hoped to give a series of short addresses, as opportunity 

 occurred, on sponges, especially from the point of view of micro- 

 scopists. Although sponges are undoubtedly animals, there is 

 some controversy as to their position in the animal kingdom. 

 Some have held that they are Protozoa ; in Germany they are 

 considered as a group of Coelenterates. Prof. Sollas styled 

 them " Parazoa." No doubt they form an isolated group, 

 and do not link on to any of the other groups very closely. 

 They have affinities with the Protozoa, but may be regarded as 

 taking a higher position. They form a large group ; it is im- 

 possible to say how many species there are, but it is an enormous 

 number, almost comparable to the insects in diversity of form 

 and structure. They are of particular interest because we can 

 trace out in them the lines of evolution, and he wished to treat 

 them from this point of view, especially as regards the spicules. 

 The Calcareous sponges include the simplest of all the types 

 (Leucosolenia). This is a tube whose wall is composed of three 

 layers. The outside one, called the ectoderm, is generally found 

 to be formed of flat cells ; these pavement cells may become 

 amoeboid. The inside layer — the endoderm — is the most 

 characteristic feature ; it is composed of collared cells. These 

 are in structure like the collared flagellate Protozoa — the 

 Choanoflagellata. Between these two layers is a stratum of 

 mesogloea with cells embedded in it, some of which secrete the 

 skeleton composed of the spicules which support the body. In 

 the Calcarea these are formed of carbonate of lime and are of 

 various shapes. In life a stream of water is taken in through 

 small pores in the body wall, and is ejected through the large 

 terminal opening or osculum. This stream is maintained by 

 the action of the collared cells. The water is swept out of the 

 gastral cavity, removing waste products, while the incoming 

 current brings in particles upon which the cells feed and also 

 oxygen for respiration. This is a very simple form, and com- 



