NOTES AND MEMORANDA. 437 



The an-angement of these foreign bodies is very irregular ; they are 

 always, however, situated in the axis of the horny fibre, and those of 

 an elongated shape have their long axis set as nearly as jjossible in 

 the direction of length of the fibre. It looks, at first sight — so com- 

 pletely is the true skeleton of the si)ouge interj)enetrated with these 

 extraneous matters — as if they were the exciting cause of the formation 

 of the skeleton ; but this is shown not to be the case, from the fact that 

 spongiolin fibres were found, exhibiting a concentrically laminated 

 structure, and quite free from foreign bodies. These latter, therefore, 

 are not essential to the formation of the horny skeleton, but are 

 probably adjuvant to it. 



The disposition of the fibres is very irregular : they exhibit no 

 distinction into vertical and horizontal fibres, but in each of the column- 

 like elevations of the sponge it is seen, in a longitudinal section, that 

 there are eight or ten more or less longitudinal main fibres, between 

 which is an irregular network of fine connecting fibres. 



The roundish pores in the ectoderm lead into irregular lacunae or 

 " subdermal spaces," from which atferent canals branch out into the 

 interior of the sponge, and finally open by minute pores into one of 

 the ciliated chambers, each of which has from twenty to thirty pores. 

 The ciliated chambers are disposed radially round the efierent canals 

 into which they o^jen directly by a wide aperture, there being no 

 intermediate passage or eiferent duct between the two. The elfereut 

 canals finally debouch into one of the wide cloacal cavities, at the 

 extremity of which is an iris-like contractile membrane serving to 

 regulate the width of the osculum. 



All those parts of the sponge which are bathed with water, except 

 the ciliated chambers, namely the external surface and the afferent 

 and efferent canals, are lined with a single layer of flat polygonal 

 cells, constituting the outer cell-layer or ectoderm. 



The mesoderm, or connective-tissue layer, consists of a hyaline 

 gelatinous matrix, with imbedded star- or spindle-shaped cells, the 

 processes of which often anastomose. The refracting granules which, 

 in most horny sponges, occur in the mesoderm surrounding the ciliated 

 chambers, are wholly absent. Contractile fibre-cells occur, as in 

 Ajoh/sina. 



The endoderm consists of the flagellate cells lining the ciliated 

 chambers : in these are contained lilac or rose-coloured granules, to 

 which the tint of the entire sponge is due. 



The morula stage was the only phase of development which the 

 author was enabled to observe. 



In Spongelia pallescens aggregations of spermatic cells were found 

 in definite cavities of the mesoderm, lined with a single layer of flat 

 cells. The ciliated embryos of this species were also examined. They 

 have the form of a cylinder, with one end slightly convex, the other 

 slightly excavated : the latter has a strong brown-red colour. The 

 body is covered by a single layer of columnar ciliated cells, surround- 

 ing a central mass having much the same characters as the mesoderm 

 of the adult. 



This species is remarkable for being infested by two species of 



