512 ME. H. M. BERNARD ON" THE AFFINITIES OF 



endosternite of the Spider) to their external cliitinous cuticles, 

 brings, I think, some order into a subject in wbich at present no 

 small confusion prevails. How great is that confusion may be 

 gathered from the recent work by Prof. Lacaze-Duthiers on 

 SalanopJiyllia *, wherever the existence or non-exiatence of an 

 ej)itheca comes into question. 



One cause of the confusion arises from the fact that too much 

 importance has been laid upon the observations which seem to 

 show that in the development of a few corals the first skeletal 

 elements which appear belong to the radial septa. I cannot see 

 that any serious importance whatever attaches to this interesting 

 observation. Given the fundamental connection between the ex- 

 ternal layer and the internal infoldiugs of that layer, we have 

 absolutely no warrant to claim that the part which appears first 

 in ontogeny must necessarily have appeared first in phylogeny. 

 Any part of the external secretion may be secondarily suppressed, 

 and no part Avould be so likely to disappear as the basal portion 

 in immediate contact vrith the substratum as soon as the septal 

 infoldings of that very region had reached any great degree of 

 development. Indeed, I do not see why we should not get 

 variation in the deposition of the secretion dependent perhaps 

 upon fine difTerences in the character of the substratum, or 

 perhaps upon difl^erences of local h-ibit. This might perhaps be 

 the explanation of the apparent conflict between the observations 

 of Lacaze-Duthiers and t. Koch as to whether the septa or the 

 basal disc begin to appear first. 



Given, however, a suppression of the basal disc, we should 

 get the appearance which led Bourne f to afilrm that the epi- 

 theca is secreted by the lower edge of the Eandplatte, and 

 appears as this latter follows the upward growth of the coral. 

 Eeference to the diagram fig. 8 will show how this appearance 

 may be explained ditferently. The epitheca may quite as easily 

 be regarded as an integral part of the whole skeleton, even 

 though its basal parts are secondarily suppressed, so that it 

 appears to be nothing but a ring of skeletal matter just below 

 the Eandplatte. There is, therefore, no fundamental disagree- 

 ment between Bourne's observation and my claim that the 

 epitheca is the primitive cup of the parent polyp. In the mean- 

 time the inability to reconcile these two observations is the 



* Arch. Zool. Exp. 3*' ser., v., 1897. 



t Quart. Journ. Micr. Sci. xxriii., 1888. 



