NOTES AND MEMORANDA. 435 



the canal like a layer of circular muscle-fibres : these have indeed been 

 described as muscular elements, but Schulze prefers to call them 

 " contractile fibre-cells." 



Amongst the ordinary mesoderm cells, rounded cells are found 

 •without definite processes, and probably to be considered as amoeboid 

 wandering cells. There also occur remarkable structures of an irregu- 

 larly rounded or knobbed form, about 10 /x in diameter, of a bright 

 yellow colour and strongly refractile. Each of these consists of a 

 number of small, globular, hyaline bodies, in close contact with one 

 another : to their presence the yellow hue of the entire sponge is 

 due. When exposed to the air, these yellow granules undergo a re- 

 markable change of colour, becoming first pale bluish grey, then pure 

 blue, and finally dark prussian blue : by this change the coloured 

 bodies become at first more transparent, but finally quite opaque. 

 The yellow colouring matter is turned brown by ammonia, and is 

 slowly dissolved by ether and absolute alcohol, readily by acetic acid. 

 Schulze considers these bodies to be accumulations of reserve material, 

 analogous to the fat-cells of other animals, and to the starch of plants. 



In the hyaline portions of the mesoderm occur very fine fibres, 

 probably comparable to the connective-tissue fibrils of Vertebrates. 

 In the neighbourhood of the ciliated chambers occur, scattered through 

 the mesoderm, numerous small rounded granules, of a whitish colour 

 by reflected light. There is no discernible bounding membrane {inem- 

 hrana limitans) either between mesoderm and ectoderm, or between 

 mesoderm and endoderm. 



The endoderm consists of collar-bearing flagellate cells in the 

 hemispherical jiortion of the ciliated chambers, into which the afierent 

 canal opens ; while the funnel-like portion, leading into the efferent 

 canal, is covered by the same tesselated epithelium as the rest of the 

 internal cavities. 



The fibres forming the skeleton of Aplysina are cii'cular in section, 

 and consist of a laminated horny cortex, enclosing a soft medulla 

 which exhibits a delicate fibrillar structure. At the apex of the fibre, 

 the lamellae of the cortex are at a considerable distance fi'om one 

 another, and have the appearance of a series of supcrj)osed glove- 

 fingers, the innermost of which exhibits perfect continuity of structure 

 with the medulla, which is thus seen to be in no way essentially 

 different to the cortex. 



In autumn and winter, rounded masses consisting of cells with 

 vesicular nuclei were found in the mesoderm of adult individuals : the 

 further fate of these is unknown, but the author considers that they 

 are probably spore-like reproductive bodies. 



2. Aplysilla sulfurea, nov. gen. et sp. — :A full description is given 

 of this genus, which differs markedly from Aphjsina in the fact that 

 the horny skeleton does not consist of a regular network of fibres, but 

 of isolated, simple or branched, terete fibres, each attached to a basal 

 plate. With regard to the migratory cells occurring in the mesoderm, 

 the author remarks that their presence proves the tisues in which they 

 occur to be a true mesoderm, consisting of actual cells imbedded in a 

 matrix or ground-substance, and answering to the connective tissue 



2 F 2 



