334 CHARACTERS AND DIVISIONS OF ALCYONARIA. 



a layer of the coral-substance. For these reasons they have all the 

 aspect of belonging to the corallum itself, and if they occurred in the 

 fossil species of the genus their real nature might very readily be 

 mistaken. 



The mode of growth of the corallum in Heliopora is peculiar. 

 The siphonopores appear to increase by means of " intermural gem- 

 mation," and not, as in the Heliolitidce generally, by fission. On 

 the other hand, the autopores, as can readily be observed in the 

 growing ends of the colony, are produced by what von Koch has 

 called " ccenenchymal gemmation." In this process — which will 

 be spoken of again in connection with Heliolites — new autopores are 

 produced by the apparent fusion and coalescence of a number of the 

 siphonopores. According to Moseley's observations on the recent 

 H ccerulea, this is effected by an arrest of growth of one or more 

 of a group of siphonopores set apart for the production of a fresh 

 autopore. " The arrested cell or cells form a central floor to the 

 new calicle, around which lies a circular zone of contiguous, deeper, 

 and older cells. The inner walls of these cells — i.e., those nearer 

 to the centre of the growing calicle — cease to grow, whilst their 

 outer ones continue to develop, and being fused together form the 

 lateral walls of the calicle. The plications in the wall of the fully 

 formed calicle are to a great extent the result of this peculiar mode 

 of growth." The conversion of a group of imperfect polypes into a 

 single complete polype is doubtless a sufficiently remarkable phen- 

 omenon ; but it is probable that, in reality, it is only a single siphono- 

 zooid which ultimately becomes developed into an autozooid, the 

 remainder of the siphonozooids concerned in the process becoming 

 aborted. An analogous phenomenon has been observed by von 

 Koch (' Zoologischer Anzeiger,' 1881) in the case of certain of 

 the Pennatulidce, in which the siphonozooids become converted into 

 autozooids. The subject is one of great palaeontological importance, 

 since the same phenomenon — as will be subsequently shown — is 

 observed in Heliolites and its allies ; and it has been contended by 

 Lindstrom that this fact is seriously opposed to the view that the 

 interstitial tubes of Heliolites are of the nature of " siphonopores " 

 rather than of " ccenenchymal tubes." The observations of Moseley 

 upon Heliopora ccerulea and of von Koch on the Pennatulida de- 

 prive this contention, however, of the weight which might otherwise 

 be attached to it. 



Since the researches of Moseley upon Heliopora carulea, it has 

 been usual to include Heliolites and its allies in the family of the 

 Helioporidce. The latter, however, possess a skeleton widely differ- 

 ent from that of Heliopora in its minute structure, while the auto- 

 pores are provided with an approximately constant number of septa, 

 the nature of which appears to be different from that of the pseudo- 



