42 THE GENUS MONTICULfPORA. 



instead of periodically, so that the wall becomes uniformly 

 thickened, instead of exhibiting alternate dilatations and con- 

 tractions. 



Apart, however, from the evidence of microscopic sections, 

 which I have sufficiently discussed above, there is sufficient 

 evidence from other sources that the tubes of Monticulipora 

 never become absolutely amalgamated with one another, as 

 they do in CJicetetes, Fischer (fig. i, d). In discussing the 

 minute characters of various species of JMoiiticiilipora in the 

 subsequent chapters of this work, I may speak of the tubes as 

 being fused together, or as having their walls amalgamated ; 

 but in so doing, I must be understood simply as referring to 

 the apparent fusion exhibited by microscopic sections. That 

 this fusion is not real, but that the walls, even in such species 

 as M. 2indulata, Nich., and AI. pctropolitana, Pand., remain 

 really permanently distinct, seems to be incontrovertibly shown 

 by the fact that fractured surfaces, so far as I have seen, in- 

 variably exhibit the exterior of the tubes. This was long ago 

 noticed by Lonsdale, and was set down by him to the fact 

 that the corallum of JMojiticiilipora increased by gemmation, 

 whereas that of Chcetetes produced new tubes by a process 

 of fission. In the latter, therefore, rough fractures exhibit 

 the interior of the corallites. Of the correctness of Lons- 

 dale's observations on this point — as observations — I can 

 entertain no doubt ; but I am not clear that the phenomena 

 are really due to the cause which he assigns. That C/icetetes 

 increases fissiparously is certain ; but I am not sure that gem- 

 mation is the regular or exclusive mode of growth amongst 

 the Monticulipom. I have formerly expressed the opinion 

 (Ann. Nat. Hist., sen 4, vol. xviii. p. 86) that certain species 

 of Monticulipora exhibited fissiparous growth ; and though 

 further observations have shown me that I relied upon evi- 

 dence which admitted of misconstruction, and that gemma- 

 tion is the common mode of increase in the Monticuliporcr, 

 I am still inclined to think that the phenomena manifested by 

 thin sections show that fission of the old tubes occurs at times 



