220 AETHUE DENDY. 



ignorant. That it does exist in many cases is beyond dispute, 

 and it is extremely interesting to learn that Bidder (21) has 

 observed in the living Sycon raphanus the coincidence of 

 the flagella of the collared cells with Sollas's membrane, just 

 as I described it in Halichondriapanicea (31). 



A curious illustration of the polymorphic nature of the 

 collared cells, is afforded by the peculiarly contracted cham- 

 bers which I described in my memoir on Grantia labyrin- 

 thica, and indicated in my drawings of the anatomy of that 

 sponge by the letter x. I have now observed the same phe- 

 nomenon in other Heterocoele sponges — viz. Ute syconoides 

 and Leucandra phillipensis — and am very glad to be able 

 to give some more exact details as to the form and arrange- 

 ment of the collared cells in these cases. Fig. 24 represents 

 a contracted chamber of Ute syconoides shown in trans- 

 verse section, and surrounded by four ordinary chambers and 

 four intercanals. It will be seen that the layer of collared 

 cells has shrunk away from the tubar skeleton, drawing the 

 mesodermal tissue after it. The collared cells themselves have 

 become radially elongated, and, owing to their having a 

 smaller area to spread themselves over, very much crowded. 

 It was doubtless this crowded condition which caused me to 

 describe them as being arranged in more than one layer in the 

 case of Grantia labyrinthica. Each cell is more or less 

 pyramidal in form, and the nucleus is situated in the apex of 

 the pyramid towards the lumen of the chamber. 



In my earlier paper (9) I endeavoured to explain the occur- 

 rence of these contracted chambers (which exhibit a very 

 different appearance from chambers in which contraction has 

 been produced by the action of the preserving fluid) by sup- 

 posing them to represent old and exhausted chambers in pro- 

 cess of dying, and destined to be replaced by the development 

 of new chambers. 



Bidder, in his very interesting "Note on Excretion in 

 Sponges" (23), has suggested a different explanation. After 

 describing the accumulation of '^spherules" in the bases of 

 collared cells, he adds, " I believe these basal spherules to be 



