REPORT ON THE KERATOSA. 53 



these cells are readily distinguishable from all other cellular elements not only by their 

 extraordinary size but also by their containing numerous, and comparatively very large, 

 granules. That a generative product when it — contrary, e.g., to the spermospores of 

 Calcarea — increases during maturation, must receive nutritious material from the sur- 

 rounding parts of the parent body is indeed obvious, but in the Porifera this may be done 

 in two ways, either by the endothelial cells playing an intermediate part, or, by means of 

 a certain modification, becoming so to speak staples for the material to be consumed by the 

 growing product. The first is the case as regards the sperm-balls, their endothelial cells in 

 all stages of development representing typical pavement-cells, and with further growth 

 gradually becoming rather flatter. Since a sperm-ball, for instance, of A2:>ly.silla sul- 

 phurea when quite mature is many times larger than the cell from which it derived its 

 origin, it must be assumed that its increase is due not only to the nutritious material within 

 the primitive cell itself, but also to the material absorbed from the surrounding elements. 

 Now the surrounding elements, viz., the endothelial cells, are neither voluminous nor rich 

 in nutritious particles ; thus the only possible conclusion is that these endothelial cells 

 having received nutritious material from other cellular elements do not retain it but give 

 it up instantly to the generative product. On the contrary, the endothelial cells 

 surrounding a developing embryo of, e.g., a Cacospongia scalaris retain the nutritious 

 particles, and it is in this property that we have also a natural explanation of the 

 striking aggregation of mesodermic cells in the neighbourhood of a developing embryo, 

 as observed and described by F. E. Schulze.^ 



Colour. — Outer surface brownish, parenchyma and skeletal fibres pale greyish. 



Habitat. — Station 135a, October 16, 1873, off Tristan da Cunha; dep»th, 7^ fathoms; 

 hard ground, shells, and gravel. 



Euspongia, Bronn. 



Spongidse with fine skeletal fibres forming a compact network, the meshes being very 

 small ; primary and secondary fibres readily distinguishable. 



Euspongia officinalis (Linnd), var. lohosa, n. var. (PI. VI. fig. 1). 



The single specimen on which this variety is founded recalls by its external shape 

 the drawing which F. E. Schulze ^ gives of Euspongia officinalis var. ttihulosa, with the 

 distinction that its basal part is not plate-like as in the latter, but massive. As in most 

 EuspongicB the outer surface is denticulated owing to the prominent primary fibres, 

 but here the conuli are very low, their height not exceeding 0"3 mm. A portion of the 

 skeleton is represented on PL VI. fig. 1 ; it is bush-like, and it must be noticed that while 



^ Zeitschr. f. wiss. ZooL, Bd. xxxiii. pi. iii. fig. 1, 1880. 2 n^l^ bj_ s^xii. pi. xxxiv. fig. 8, 1879. 



