1910.] 



PROM MERGUI AECHIPELAGO. 



819 



Considex-able variation occurs also in the proximity of the hydro- 

 thecc-e of the same lateral series, for while a marked gap separates 

 some — usually on the distal portions of branches — in many cases 

 the upper portion of one hydrotheca is pressed against the base of 

 the next (cf. PI. LXXVII. figs. 12 «, 12 b). An abnormality in 

 the formation of the hydrothecje is worth noting. Occasionally, 

 probably after some accident to the branch, the hydrothecoe first 

 formed thereafter, while normal so far as the adnata portion is 

 concerned, have an exceptionally long portion free (0-77 mm., as 

 contrasted with the average O'l mm.), this part being tubular, 

 recurved, and having a rather indefinite margin. Its successor 

 is less, though still abnormally large, and the diminution con- 

 tinues until the normal size is reached after five or six hydro- 

 theca-pairs (text-fig. 79). 



Text'fig. 79. 



Abnormal hydrothecae of Sertularella quadridens, X 20. 



The pinnfe, each of which arises beneath a hydrotheca, are 

 regularly alternate, three hydiotheca; being interposed between 

 two pinna; on the same side. In one case a branch, of second 

 degree, was observed to spi-ing from the lumen of a hydrotheca. 



The structures of the soft parts of the species, to which I have 

 seen no reference, show points of interest. The coenosarc of the 

 stem is an-anged in a varying number of longitudinal strands, 

 usually three or foui', which are connected irregularly by anasto- 

 mosing canals, and which, with their connections, line the perisai'c. 

 In the branches the structure is less compliciited. There, two 

 large longitudinal coenosarc tubes are to be distinguished, one 

 running along each side of the branch, and tlireading its way 



[21] 



