280 Mr. H. J. Carter on the Nomenclature 0/ Clathrina. 



development on the under surfaces of rocks here which are 

 left micovered by the tide for several houi'S daily. 



The central and oldest portion, too, very frequently becomes 

 elongated, from its pendent position, into a mammiform process 

 as large as the top of a man's thumb, which appears to be 

 more or less eifete (exhausted in the middle, like some spread- 

 ing fungi), while the circumferential parts are the best deve- 

 loped for description, and are most likely to die with their 

 vents or oscules open — a contingency which has led previous 

 describers occasionally to pass them over unobserved. 



From the papillary eminences where the oscules are situated 

 the tubulation branches off in all directions, anastomosing 

 with that which belongs to the neighbouring divisions, and 

 thus forming a continuous network drained by the several 

 oscules, just as the canal-system in the solid sponges. 



Here, then, the only difference between the network of 

 Clathrina and that of the solid sponges appears to be the ab- 

 sence of the interstitial matter which, uniting the branches of 

 the canal-system together in the latter, gives them their solidity. 

 Thus it would appear that the canal-system in both does not end 

 in open mouths anywhere except at the oscules, and that what- 

 ever gets into it must naturally pass through the pores and 

 be very minute, as their capillary extremities only end in 

 anastomoses. In this way probably we may picture to our- 

 selves the excretory canal-system of all sponges. 



Of the colour, too, of this sponge there would appear to be a 

 difference of opinion : thus Schmidt's specimens were sulphur- 

 yellow, Lieberkiihn's [aj). Sdt.) colourless, Mrs. Buckland's 

 {ap. Bk.) crimson, Johnston's bluish grey or white changing 

 to yellowish brown when dried or immersed in fresh water — 

 which latter is a very good test for the species, as will pre- 

 sently be shown. 



The specimens here are whitish or bluish grey, with occa- 

 sionally sulphur-yellow, but with no structural difference that 

 I can detect ; so I conclude that both colours belong to the 

 same species. I have never seen it of a crimson colour ; but, 

 as I have before stated respecting the bright scarlet colour of 

 Esperia macilenta^ it would be worth inquiring whether these 

 bright colours occasionally assumed by sponges have not 

 something to do with the reproductive process. 



We must not forget, however, that in some instances 

 the colour may be owing to the presence of a foreign organism 

 or parasite. 



Thus I have just observed, in a portion of Halichondrta 

 incrustans found here last September, growing on the rocks, 

 that, although generally of its natural or yellowish sponge- 



