CEKTAIlSr STICHODACTYLTTSr^ TO THE MADEEPOBAEIA, Q4i7 



fibrillar" structure." And again (1887 a, p. 6) : — " The meaogloea 

 in Mussa is perfectly structureless." 



Fowler records similar conditions for most of the corals 

 studied by him. In all the coral polyps I have examined the 

 nature of the mesogloea is of this simple character ; the layer 

 stains slightly with borax-carmiae, and an included cell is but 

 rarely observed. Though such a difierence between the mesoglcea 

 of Actiniaria and Madreporaria is perhaps of no great morpho- 

 logical significance, being only one of degree in the number of 

 cells included, yet it is a very marted distinction when examining 

 sections of representatives of the two groups. 



Of the anemones, Gorynactis is the only form I have met 

 with in which the mesogloea is nearly perfectly structureless, 

 exactly recalling that of coral polyps. Unless slightly stained 

 its presence is not easily detected in the clear field of the 

 microscope. Both C. myrcia and G. australis agree in this 

 respect. The mesogloea of Bicordea and Blwdactis contains 

 numerous cells, as iu other Actiniaria, though they are not by 

 any means so plentiful in the former as iu the latter. Prom all 

 accounts, the mesogloea of GeriantJius appears to be clear and 

 homogeneous. 



Mtjsculatfee. 



In most anemones the musculature is well developed, and 

 supported upon more or less complicated folds of the mesoglcea, 

 or may ultimately become buried within it. Distally a con- 

 cenbration of the circular endodermal muscle, known as the 

 sphincter muscle, generally occurs in the column-wall, but 

 forms devoid of it are not rare. The musculature of the Madre- 

 poraria is by contrast but feebly developed, the mesogloeal 

 foldings rarely attaining a complicated outline. In such a large 

 form as Fungia, however, the muscle-layer is stronger, the meso- 

 gloea becoming arborescent for its support. A sphincter muscle 

 in coral polyps was first discovered by Fowler (1888, p. 12) in 

 S])henotrocMis rubescens. Compared with that of most ane- 

 mones, it is of a very weakly diffuse character. Fowler also 

 states that in the same species both the longitudinal and oblique 

 muscles of the mesenteries are exceptionally well developed, the 

 former applied to such arborescent pleatings of mesogloea as 

 have been described among both Madreporaria and Hexactinige. 

 I have lately met with a diffuse endodermal sphincter muscle, 



46* 



