166 ARTHUR DENDY. 



which they are directed more or less at right angles, so that 

 the chambers certainly exhibit a more or less radial arrange- 

 ment. At their proximal ends the chambers open into wide 

 and long exhalant canals, which converge towards the osculum. 

 The distal ends of the chambers are covered over by a thin mem- 

 brane, strengthened by spicules and perforated by numerous 

 inhalant dermal pores. These pores lead into a series of quite 

 irregular spaces lying between the branching chambers. These 

 spaces represent the inhalant canals, and convey the water to 

 the prosopyles in the thin walls of the chambers. In all speci- 

 mens which I have seen of L. simplex and in one of L. cla- 

 vatus (4) the mesoderm is feebly developed, so that the dermal 

 membrane, the walls of the chambers, and the walls of the ex- 

 halant canals are all very thin, and the entire sponge has 

 consequently a soft and delicate texture. In one of the speci- 

 mens which I have referred to, L. el a vat us, the mesoderm 

 is very strongly developed ; the sponge thereby acquires a 

 dense and solid texture, and the canal system is correspondingly 

 reduced in dimensions. This strong development of the meso- 

 derm is perhaps to be associated with the fact that the speci- 

 men contains very numerous embryos; for the normal condition 

 of the genus appears to be one with all the canals and chambers 

 thin-walled. 



This genus, as already indicated, does not appear to come 

 into what may be called tiie typical series of Heterocoela; and its 

 relationships and systematic position will be discussed later on. 

 Though I do not suppose that it has ever passed through a 

 Sycetta stage in its history, it is easy to see how its canal 

 system may have been derived from a radiate ancestral type, by 

 modification along the lines suggested above. 



Sycetta. 

 The simple form of canal system met with in this genus has 

 already been described. If we exclude from the genus 

 Haeckel'is S. strobulus, S. cupula, and S.stauridia, which 

 are all corticate species, and include, as von Lendeufeld (10) 

 has rightly done, Sycetta (Sycaitis — H.) conifera, we are 



