Study of Madrepor avian Types of Corals. 221 



trabecular axes in the median septal plane. Each member of 

 a successive series of fascicle " pairs " or " groups " in a 

 trabecula is called bj the author a trabecular part ( Trahekel- 

 glied). The ^\fascicle " may be regarded as the structural 

 unit of the coral-skeleton. Two or more fascicles combine to 

 build up a " trabecular part.''"' And the differences in the 

 relative arranyement of trabecidar parts determine the endless 

 varieties of skeletal form icithin the Madreporaria. 



The author has subjected the following- typical genera to a 



detailed microscopic investigation : — Galaxea, Mussa, Heli- 



astrcea, Goniastrcea, Montlivaltia^ Thecosmilia ; then Fung ia, 



Siderastrcea, Lophoseris ; further, Eupsammia^ Haplarcea ; 



and, lastly, Turbinaria^ Actinacis^ Madrepora^ and Porites. 



This research enables the author to state that different types 



of septal structure are characteristic of different groups of 



Madreporaria. The differences relate to the microscopic 



structure of the trabeculse and to the arrangement of trabeculas 



in the plane of a septum. It is impossible here to do more 



than indicate the line of research. Turbinaria is an example 



of an extremely simple structural type. The component 



trabecula; are small, uniform in size, and directed all in the 



same way, obliquely or almost horizontally inwards from tfie 



periphery of the septum to the inner edge. The fascicles are 



paired, and their axes never bend out of the median septal 



plane. Galaxea has a septum whose trabeculie bend right 



and left from a definite area of divergence in the septal plane. 



The individual trabecular are large, vary in size, and the axes 



of the paired fascicles bend out of the median plane towards 



the opposite surfaces of a septum. The septum of Mussa is 



composed of a number of broad ridges, elliptical in section 



and ending at the upper edge of the septum in broad " spini- 



form teeth." The author shows that each " spiniform tooth " 



is itself finely serrated, and that the serr^e represent apices of 



trabecular. In short, a single broad ridge of the Mussa sepfwm 



is the precise homologue of the complete Galaxea septum^ being 



built up of fan-shaped groups of trabeculge diverging right 



and left from the middle area of a ridge. Again, Fungia has, 



like Mussa, a septum composed of a number of ridges ; but 



the trabeculge in each ridge have a course almost parallel with 



one another. The emergent fascicles are thus so close that 



coalescence inevitably takes place ; the soft parts of the polyp 



clothing the ridge are pushed outwards at the prominent 



middle part of the ridge, and readily give rise to synapticular 



union between septa. Further reference to this part of the 



work must be omitted here. 



The author observed in sections of recent types that a larger 



