104 Mr. H. J. Carter on the Growth of Stromatopora. 



Here I might observe that the infundibular structure of 

 Syringopora appears to be allied to the diaphragms produced 

 by the " annulation " (or circular constrictions of the tube) 

 which is such a very common feature among the flexible 

 Hydroids, and thus frequently appears in a modified form in 

 the tubes of Caunopora — the effect of such constrictions being 

 to force the coenosarcal tube into the centre of the flexible 

 horny one, which in Syringopora geniculata, from the tubular 

 processes of the infundibula passing into each other, gets 

 beyond a mere constriction, and thus sometimes becomes a 

 continuous calcareous central canal. 



The tubes of Caunopora are, for the most part, straight or 

 slightly flexuous, equal in calibre, unbranched and parallel in 

 their course, and, although hardly ever appearing otherwise 

 than in short fragments, were found by Mr. Champernowne, 

 in a weathered-out instance from "Pit-Park Quarry," to attain 

 If inch in length ; so that it may fairly be assumed that, if 

 it were not for their slightly flexuous course, they would be 

 found to be continuous throughout, i. e. from their origin to 

 their termination. But it by no means follows that because 

 the main tubes pursued this course they were not often united 

 by smaller ones, after the manner of Syringopora, from which 

 it becomes almost impossible to separate them in every respect 

 when all their structural varieties are taken into account. 



Seeking among the flexible Hydroids for one that would 

 afford analogous features, we find it in Tubularia inclivisa, 

 which grows so luxuriantly on our coasts, of which the Rev. 

 T. Hincks (Hist. Brit. Hydroid Zoophytes, 1868, vol. i. 

 p. 115) gives the following characters of the polypary, viz. :— 

 " Clustered, simple, erect, without annulation, narrowed and 

 twisted at the base, horn-coloured, rising to a height of from 

 6 to 12 inches." The tubes are about l-16th of an inch in 

 diameter, and seldom divide except near the hydrorhiza, which 

 consists of " twisted and interwoven tubes often agglomerated 

 together." But then there are not only other species of Tubu- 

 laria which divide throughout much oftener, but one, viz. 

 T. bdlis } which is annulated throughout (op. cit. Atlas, 

 pi. xxi.). 



Now such Hydroid Zoophytes, whether flexible or calca- 

 reous, if overgrown with Stromatopora, would represent Cauno- 

 pora) and if we require a similar instance of commensalism, 

 it is afforded in Stephanoscyphus mirabilis, which Prof. All- 

 man found on the south coast of France, and describes as 

 consisting of a horny sponge traversed by " a congeries of 

 tubes which penetrate the sponge-tissue and open on its sur- 

 face, united by a common tubular plexus towards the base." 



