lo llu' two lasl iiu'iitioncd writers, Calvct andHaiiner look upon calcificalioii 

 as a cuticiilai rormalion, but while Ca 1 v e l' tliinks that calcification at any rate 

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

 following ohservalioii of Harmer- seems to suggest that he is inclined to share 

 Nitsche's view of the calciiication as j)roceecling in the central part of the 

 cuticle: in incinerated specimens the lateral walls of neighbouring zoa-cia may 

 appear separated from one another by a narrow slit in jjlace of the laised linc<'. 

 This is in fact the edge of a chitinous layer separating contiguous zoa-cia, and 

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

 by Nitscbe of the calciiication of the zcxj'cia of Mcinbrdiiipord membi<uuict'<t, 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 »cell-theory« is the one which explains the different plie- 

 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 

 sjjinous processes on the outer surface in a number of species (e. g. in llolo- 

 porelld columnaris) as well as on the inner (e. g. in Menipea roborala Hincks and 

 M. lifiiilata 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 very dilTerent resistance which the calcified skeleton is able to 

 offer against breaking and grinding shows sulTicienlly Ihat the comj)aclncss and firm- 

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

 of Sclerodomulae and Releporidae just as we find the weakest in the families Bicella- 

 riidae, Flustriilae, Onchoporidae and in certain species of Membntiiijidrd. U we 

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

 Meinbranipora membranaced, Electra pilosd, Flustra Cdrbdsea, Dendrobeania miirrdi]- 

 ana and Oinliopora Siinldiri) under a raliier liigh 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, liowever, the same wall may 

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

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

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



' 9, pp. 29 & K;.-); * 17. p. 227. 



1* 



