20 G. LINDSTRÖM, HELIOLITID^. 



to that extent as Bourne postulates. There is reduction and new growth. The septa 

 are not a result from the ai'rested growth of twelve environing tubuli, but from the altered 

 growth of the central tubuli and they are not formed all at once. In stage III there 

 are seven and in stage IV nino. Moreover in Heliol. interstinctus there are only nine 

 tubuli in the beginning partaking of the gemmation. 



Most interesting and remarkable is to find in the same specimen of Hel. porosus 

 the seven stages of the progress of the_ gemmation and side by side with it a fuUy 

 developed calicle which is changing step for step in a quite opposite direction or decaying, 

 dying out by being by degrees changed again into coenenchyma, out of which it had 

 originated, in the same way as the budding new calicle beside it. The particulars are 

 given in the description of Heliol. porosus. 



If meeting ^vith a calicle like the left one in section five (pl. ii tig. 37) alone, without 

 connection with any precedent or subsequent stage, it must indeed be very difficult, if not 

 impossible to decide whether it is a calicle in progress or in regress, so nearly do both these 

 changes resenible each other. We can consequently say that a Heliolitidean calicle origi- 

 nates from the coenenchjana but also in decaying returns to coenenchyma. 



In a manner quite contrary to the generating agency, as a destructive one, the 

 coenenchyma invades the calicles immersed in it. Through its exuberant growth it some- 

 times encroaches upon the calicles, covers them and kills them. (See pl. i tig. 20, 21.) 

 The struggle between the coenenchyma and the calicle is to be seen in such longitudinal 

 sections as figured on plate ix f. 24 or more stränge on pl. x fig. 23, where, if I under- 

 stand it rightly, calicles have been över whel med by the coenenchyma twice and new 

 calicles grown up as many times. If it be so, it is a new and curious instance of the 

 observations that a part of an organism can subdue and annihilate a more important and 

 central part. Generally the coenenchyma has been regarded as something alien to the 

 calicles, as without any connexion with them. But we now see them in a continuous 

 intercourse, in reciprocal action, the coenenchyma is an outgrowth from the calicles and 

 the calicles on the other hand bud out from the coenenchyma. 



This kind of propagation forms one of the most serious objections which militate 

 against accepting the hypothesis of dimorphism in the Heliolitida?, so eagerly contended 

 for by NiCHOLSON and his followers. Long before 1883 when my observations on the 

 coenenchymal gemmation were first published in abstract, ' I had seen this mode of 

 propagation in Heliolites and Plasmopora and alread}' in 1876 the first figures repre- 

 sentiiig this process were drawn. During the voyage of »Challenger» Moseley in 1875 

 discovered a similar mode of gemmation in Heliopora and his observations were published 

 the following year.^ He says that »new calicles are developed by the arrest of growth of 

 one or more cells (-- coenenchymal tubuli) .... which .... form a central floor in the 

 calicle». The appertaining figure (pl. 9 f. 17), however, shows, as it seems, in the bottom 

 of the calicle several Intact coenenchymal tubuli. In turning to specimens of Heliopora 

 to consult them in this case, it is very easily seen that the calicles originate from the 



1 Oborsilurische Korallen von Tshau-Tién, in Richthofen's Cliina. Bd 4, p. 50. 



^ Oa the structure of the Alcyonariau Heliopora coerulea etc. p. 99 & 120 in Philos. Tr. R. Soc. 1876. 



