172 Reviews — Miss Maria Ogilvie, D.Sc. — 



terminology. It is true that when any portion of the basal body- 

 wall resting upon a single layer of the secreted skeleton leaves 

 that layer, it has undoubtedly been pulled off by the growth 

 of the skeleton raising up the whole animal. In this case the skin 

 typically proceeds to secrete another layer as soon as it has come to 

 rest, these secondary basal layers forming '* dissepiments " or 

 " tabulee," according to their position in the calyx. It appears as 

 if this active withdrawal of the body from its flat skeletal floor has 

 led Miss Ogilvie to attribute the formation of septa also to active 

 infoldings of the wall. Is there any evidence for this? My own 

 impression was, that the active secretion of solid matter by the 

 aboral ectoderm was prior to the formation of septa, and thus 

 sufficient of itself to account for the septa. The more active 

 secretion of the ectoderm in the bases of the intermesenterial 

 chambers would cause the passive pushing in of the aboral wall by 

 radially arranged deposits. Wherever, in fact, for any cause, the 

 secreting activities are increased the wall is passively pushed in by 

 the hard matter deposited. The very disordered order of the centres 

 of calcification revealed to us by Miss Ogilvie's sections is, it seems 

 to me, more in keeping with this suggestion than with what appears 

 to be Miss Ogilvie's own view of the matter. But, however clear 

 and correct Miss Ogilvie's own views on this subject may be, she 

 certainly leaves the reader in doubt as to whether the invagina- 

 tions of the body-wall are active or passive. This is not by any 

 means a trifling point, for morphology is a vain pursuit without 

 physiology. 



The discarded calcified cells, then, are the bricks for the building 

 up of the various parts of the skeleton, and while they are laid 

 fairly regularly in layers ("growth lamellae ") over one another, 

 these layers never seem to start quite regularly except wlien the 

 deposit is single, e.g. for the formation of a dissepiment. On the 

 other hand, whenever these bricks are going to bulge up the skin, 

 which secretes them, for the formation of a septum, they seem to 

 start, not along continuous lines, but from single points round which 

 they radiate. These dark points are " the centres of calcification," 

 while the cells with their crystalline contents form radiating bundles 

 of fibres called " fascicles." Sections of septa show fairly regular 

 groupings of the dark centres with their fascicles. A ti-abecula, 

 according to Miss Ogilvie, is formed by a continuous series — single 

 or multiple — of such dark centres rising from the base towards the 

 upper edge of the septum, straight up or bending towards its inner 

 Of outer edge, or sometimes even horizontally arranged : the distal 

 ends of these trabeculae run out into teeth or septal spines, and so 

 on : for the many interesting details the reader must consult the 

 original work. 



Miss Ogilvie, whose merit it is to have patiently examined for 

 these details of fine structure a long series of types, recent and 

 fossil, is able to announce that this method of building up the 

 skeleton is the same to-day as it was in the earliest known 

 fossil; growth lamellae, fascicles, and trabecular are fixed elements 



