984 MR. B. KIBKPATRICK AND DB. J. METZELAAR 



animals. Exactly the same is the case with our Polyzoon. The 

 simple colonies from one station have all changed into m^icrocosms 

 of sessile invertebrate life. Large specimens of Lithodomus 

 easily lodge in the thick, limestone-like wall without touching 

 their motor-pagurid. There are the big colonies of a compound 

 ascidian {Distomus sp.), purple barnacles, bushy hydroids upon the 

 Polyzoan wall (PI. II., hg. 14). Although very interesting from 

 an oecological point of view, we shall not describe these compound 

 colonies as they do not show constant features, the original 

 Paguro-Polyzoan association having lost its exclusive character. 

 Meanwhile it illustrates the fact that mobility of substratum is 

 favourable to diverse forms of sessile animal life. 



By the way, we may notice one rather striking fact. Although 

 the weight of its limestone house with weeded roof must become 

 a nuisance to the Hermit, however powerful it may be, let us 

 mention one point in favour of its security. In one of the 

 hydroid tufts a spawning Sepia has glued several eggs. Sp 

 this professional crab-eater remained unconscious of the close 

 proximity of its prey, and the most critical sceptic must admit 

 that this argument, taken from nature itself, is stronger than any 

 aquarium experiment as to the efficiency of this pagurine mode 

 of life. 



As a counterpart to this, we may add that remains of Eupa- 

 gurus hernhardus are often found in the stomachs of Cod from 

 moderate depths in the North Sea. 



DescrijMon of the Folyzoon, based upon 4| adult and 3 young 

 samples sent to the Natural History Museum, London. 



A glance with a good lens at once shows the Polyzoon to be a 

 member of the great Membraniporidan group. The surface of 

 the zoarium is covered with a membrane, which can be peeled 

 off. The zooecia are arranged in straight, longitudinal rows, the 

 latter every now and then bifurcating. The zooecia are not 

 abreast transversely, but in qiiincunx. A five of diamonds in 

 cards, with the pips uniformly enlarged till they nearly meet, 

 would illustrate the plan. 



The zooecia (PI. I. figs. 4, 5, 6) are oval, and on an avei-age 

 0-6 mm. long and 0-3 mm. wide in the middle. The margins of the 

 zooecia in well-preserved material are mapped out by dark brown 

 membranous or chitinous lines. Busk calls attention to similar 

 " brown lines " in his description of Alemhranipora denticidata 

 Busk. 



The calcareous margin is strongly granulated, and slopes 

 inwards and downwards to a finely serrated edge bordering the 

 oval opesia. 



At the proximal or basal end of each zooecium and immediately 

 below the opesia there are two triangular, flattened, hollow 

 tubercles, separate in the young stage, but joined into a single 

 rectangular block in older zooecia (figs. 4, 5, 6). The brown line 

 separately surrounds each triangular tubercle and also each 

 rectangular block. 



