66 



MR JAMES RITCHIE : SUPPLEMENTARY REPORT ON 



Between the hydroclade and the internode process on which it is set occur from one 

 to three athecate internodes. The hydrorhizal tubes are close-set, are compressed from 

 above downwards, and are supported by thickenings of the perisarc which project into 

 the interior of the tube. Somewhat similar thickenings I have already seen in the 

 hydrorhiza of a species of Podocoryne (Eitchie, 1907/^' p. 499) which was growing on 

 a minute shell. In both cases it is possible to imagine that the thickenings may be 

 in some way correlated with the peculiar substratum upon which the specimens are 

 growing, for either on a small, readily tossed shell, or on the ever-moving appendages of 

 a Crustacean, hydrorhizal tubes would be submitted to a great amount of buffeting and 

 rough usage. Reaction to such abnormal external factors might result in abnormal 



Fig. 7.— Plurmdaria lagenifera, va.r. sepfifera. (rt.) Portion of stem and hydroclade. x 100. (6) Base of stem 

 arising from complicated hydrorliizal growtli witli scattered nematotlieca=. 



strengthening of the walls. Should such a supposition be well founded, the thickenings 

 in the hydrorhizal tubes could have little systematic value. Frequent nematophores, 

 similar in structure to those on the remainder of the colony, arise from the hydrorhizal 

 tubes at irregular intervals, but always near their borders. 



The differences between this form and P. lagenifera in size, in habit, in the intensity 

 of the internal septa, in the absence of a nematophore on each stem internode, and in 

 possessing chitinous thickenings in the hydrorhiza, I do not consider sufficient to warrant 

 the formation of a new species. 



Measurements : — 



(rot. SOC. EDIN. trans., vol. XLVII., 88.) 



