MATKRIALS FOR A MONOGRAl'H OF THE ASCONS. 497 



interior. (4) That the pore-cells are eminently contractile, 

 and when contracted have received very different interpreta- 

 tions from different authors. 



Connective-tissue Layer. — This consists of the spicules 

 and their secreting cells embedded in the structureless jelly 

 which constitutes the greater part of the body-wall. 



The triradiate spicules have each a single cell applied to the 

 extremity of each ray. These spicule-cells, as we may term 

 them shortly, have the protoplasm very clear and almost free 

 from granules. The nuclei are slightly smaller, and stain more 

 deeply than those of the flat epithelial cells, appearing oval in 

 profile view, circular in surface view (fig. 14). 



I desire to correct the statement made by me in a furmer 

 paper, to the effect that each spicule in coriacea had a nucleus 

 at the extremity of each ray, and a fourth at the confluence of 

 the rays (1892 [1], p. 265). When a spicule ray crosses the 

 centre of another spicule an appearance may be produced of a 

 cell at the centre of the spicule, which is not, however, the 

 case. There are no other cells on the fully formed spicule 

 than the three at the extremities of the rays. "What applies to 

 the triradiates applies also to the basal rays of the quadri- 

 radiates. The apical rays of the quadriradiates have, as we 

 shall see, a variable number of nuclei upon them. The large 

 monaxons of many species of Clathrina are covered by a 

 number of cells, but exactly how many is a point very difficult 

 to determine. 



As we shall describe fully below the origin of the spicule 

 cells, it is not necessary to enter into a further discussion upon 

 them here. 



Amoebocytes. — The wandering cells are very important 

 and conspicuous elements of the sponge body. They give rise, 

 as is well known, to the sexual elements, and their complete 

 history will, I believe, furnish some points of considerable 

 interest when worked out. At present, however, I am still far 

 from being able to give a complete account of them, and will 

 therefore content myself with describing them as they occur 

 ordinarily in the aduU sponge. 



