to the two last mentioned writers, Calvet and Harmer look upon calcification 

 as a cuticular formation, but while Calvet' thinks that calcification at any rate 

 in the Cheilostomata takes place through the whole thickness of the cuticle, the 

 following observation of Harmer^ seems to suggest that lie is inclined to share 

 Nitsche's view of tlie calcification as proceeding in the central part of the 

 cuticle: »hi incinerated specimens the lateral walls of neighbouring zocecia may 

 appear separated from one another by a narrow slit in place of the '>raised line«. 

 This is in fact the edge of a chitinous layer separating contiguous zocecia, and 

 prolonged into the membranous epitheca. This agrees with the account given 

 by Nitsche of the calcification of the zocecia of Membranipora membranacea, in 

 which calcareous matter is said to be formed in the middle of the chitinous 

 ectocyst, part of which is left on each side of it«. We shall return later to this 

 statement. As I have not been able to examine living material I do not consider 

 myself qualified definitely to decide which of the views is the right one, still it 

 seems to me that the »ceU-theory« is the one which explains the different phe- 

 nomenona, which the calcification presents, in the easiest and most natural way, 

 and it seems to me especially difficult to explain the presence of such solid 

 spinous processes on the outer surface in a number of species (e. g. in Holo- 

 porella columnaris) as well as on the inner (e. g. in Menipea roborata Hincks and 

 M. ligulata Mac Gill.) by the aid of the cuticular theory. 



We may now consider a number of differences which the calcification pre- 

 sents, and to begin with we may distinguish between more or less compact or 

 firm calcifications. The veiy different resistance whicli the calcified skeleton is able to 

 offer against breaking and grinding shows sufficiently that the compactness and firm- 

 ness can be different, and the firmest skeleton is undoubtedly found in the families 

 of Sclerodomidae and Reteporidae just as we find tlie weakest in the families Bicella- 

 riidae, Flustridae, Onchoporidae and in certain species of Membranipora. If we 

 regard parts of the skeleton of certain, very slightly calcified species (e. g. of 

 Membranipora membranacea, Electra pilosa, Flastra carbasea, Dendrobeania murray- 

 ana and Onchopora Sinclairi) under a rather high magnification, it shows a 

 grained or dotted appearance, but under a very high power (immersion) it dis- 

 solves into a dendritic network, the meshes of which enclose numbers of small 

 uncalcified spots, which give a reddish light. Sometimes, however, the same wall may 

 show more or less calcified parts. We thus find in Dendrobeania murrayana that 

 the part of the basal wall, wiiich touches the distal wall, is much more calcified 

 than the other part, and in the middle of the basal wall in Escharoides Jacksoni 



' 9, pp. 29 & 165; ^ 17, p. 227. 



1* 



