SOLITARY CORALS. 229 



Another singular fact is the presence of only one pair of directive mesenteries, the 

 absence of the second pair being obviously explained by the division of the parent 

 at right angles to the long axis of the calicle, whereby one pair of directives 

 remained in the one, and the other pair in the other of the offspring. The 

 existence of the single pair of directives in a coral which has doubled itself by a 

 single act of fissiparity confirms the conclusion I arrived at in an earlier paper (5), 

 that the absence of directives in many corals is to be explained by the fact that they 

 have multiplied by fission. 



To deal briefly with other points in the anatomy of the polyp. The external body 

 wall, as Fowler describes, rests upon the echinulations of the ccenenchyma, and 

 there are no peripheral continuations of the mesenteries. The tentacles are all 

 endoccelic, and therefore correspond in number to the endosepta. In contraction they 

 are introverted, and in this condition are doubled over the inner edges of the 

 endosepta. Thus they are situated nearer the mouth than in Heterocyathus, and the 

 peristomial area is correspondingly reduced. The primary and secondary tentacles 

 form a circle nearest to the mouth, the remaining orders form circles at greater 

 distances from it, and it follows from their relations to the endosepta that the 

 tentacles of different orders alternate with one another. In H. michelini the 

 tentacles are covered with well-developed batteries of nematocysts ; in H. multilobata, 

 according to Fowler, they are not. 



There is a short, but distinct stomodasum, and I think that I found traces of a 

 sulcus (gonidial groove), but of this I cannot be certain, as both my specimens 

 suffered partly from the attacks of boring sjjonges, and partly from the fact that 

 grains of quartz sand were lodged in the angles of the mouth and produced imper- 

 fections in my sections in those regions. However this may be, the circulation of 

 water in the complex chambers in which the lower parts of the mesenteries are 

 lodged is provided for by means similar to that described in Heterocyathus. The 

 filaments of the primary and secondary mesenteries form broad sinuous bands in the 

 upper part of their courses, and it is only deep down in the coral that one meets 

 with the characteristic kidney-shaped sections of mesenterial filaments. The number 

 and arrangement of the mesenteries has been sufficiently described. As far as I 

 could determine, all the mesenteries are fertile, but in the undivided specimen of 

 which I made sections the quaternary mesenteries, especially those in the lateral 

 chambers, were in advance of the remaining orders as regards the maturity of ova 

 contained in them. The ova, and as far as I could make out in a series of loncd- 

 tudinal sections the testes also, are embedded in the mesoglcea of the mesenteries in 

 the manner figured by the Hertwigs for Actinia, and do not hang from the sides of 

 the mesenteries in follicles as in Heterocyathus. 



Histology. The external tissues were very well preserved, but the reagents 

 had not penetrated well, and the endoderm and mesenterial filaments were in 

 consequence macerated and of little use for histological examination. 



