222 Miss M. M. Ogilvie — Microscopic and Systematic 



amount of organic cell-material was usually present near the 

 median plane of the septum than towards the lateral surfaces. 

 This she believes may be attributed to the greater rapidity of 

 the calcareous secretion and the less complete calcification of 

 the calicoblasts present at the doubled upper edges of septal 

 invaginations. In fossil matei'ial secondary changes render 

 this central part of the septum more or less conspicuous on 

 account of the breaking down of organic products, or some- 

 times the complete replacement by infiltrated salts. The 

 author strongly contends that there is no basis for the assump- 

 tion of a ^^ primary septum " in the middle plane of a septum 

 in the sense at present accepted by most palaeontologists. On 

 the contrary, the authoi-'s sections show that i\\Q Jihro-crystal- 

 line structure of the septum is the same throughout its whole 

 thickness, essentially that of a double system of thin calcareous 

 lamelloi, either smooth or fluted, and corresponding to a 

 deposit from opposite flaps of an invagination. 



The author's investigations afford many new microscopic 

 facts of structure, testifying that the growth in height of the 

 polyp is accomplished at certain growth-periods, between 

 which pauses ensue. During each growth-period a varying 

 number of the calcareous lamellaa, " growth-lamellge," are 

 laid down, and these always appear in intimate union with 

 one another. Again, regular curves or lines of growth are 

 evident on tlie septal surfaces, marking the intervals between 

 successive growth-periods. The space between two growth- 

 curves or lines on the septal surface represents the part of the 

 septum built up in one growth-period, and it has been called 

 by the author a septal growth-segment. An important obser- 

 vation is that the extra length added to a single trabecula in 

 one growth-period is invariahly one trabecular part\ this 

 length varies in the trabecula? of one and the same septum, 

 being greatest at the exsert portions near the wall. 



Granulations mark tlie surfaces of trabecular parts. Ed- 

 wards and Haime applied the term " synapticula " to the inter- 

 septal bars in Fungia and its allies, and described the synap- 

 ticula as formed by coalescence of granulations from opposite 

 surfaces of neighbouring septa. The author demonstrates 

 that in Fungia the granulations seldom meet across interseptal 

 loculi ; but a continuous calcareous deposit is formed in a 

 special invagination of the interseptal parts of the aboral 

 body-wall. Together with a number of observations on other 

 synapticulate types, this has led the author to accept a distinc- 

 tion made by Fratz, and hitherto discredited in the literature. 

 Pratz proved that the fossil Fungid subfamily of Thamnas- 

 traiinai had synapticulre forip.ed by coalescence of granulations. 



