REPORT ON THE DEEP-SEA KERATOSA. 



45 



Hydroids belong partly to the Campanulariae (Halisiphonia, PI. IV. fig. 9), partly to the 

 Tubulariae (Stylactella, PI. II. figs. 6, 7), partly to a larger Hydroid with annulated 

 tubes, the true position of which I could not make out (Eudendrium f, PL IV. fig. 4). 



Eggs and Larva?. — Amoeboid eggs, with a large clear germinal vesicle and a 

 dark germinal spot (PI. V. fig. 5, e), partly in segmentation, were found scattered in 

 the mesoderm of Psammopliyllnm Jlustraceum (PI. IV. fig. 5). The same specimen 

 contained larger dark ovate bodies composed of granular cells, which probably were 

 decomposed or badly-preserved gastrula larvae, similar in size and form to those of other 

 Spongelidae. 



Genus 7. Cerelasma, n. gen. 1 



Definition. — Spongelidae with reticular spherical or tuberose body, composed of 

 numerous anastomosing branches, each branch supported by a peculiar reticular 

 framework of thin spongin-lamellge. These, as well as the maltha, enclose numerous 

 xenophya, which are usually enveloped by a spongin-sac. 



The genus Cerelasma differs from all the Keratosa hitherto described in the peculiar 

 shape of the Keratose skeleton, which is not composed of cylindrical or roundish fibres, 

 but of flat and thin horny lamellae. These are branched, and the branches unite and 

 form a framework in the most irregular manner. The xenophya possess usually also a 

 saccular envelope of spongin, and are partly enclosed in the maltha, partly in the lamellae 

 of the framework. This is expanded between the tubular branches of a reticular dark 

 coloured symbion, probably in all cases the hydrorhiza of a symbiotic Hydroid (Stylactis 

 or another Spongoxenia). 



The peculiar structure of Cerelasma may be best understood anatomically, if we 

 compare it with that of a human liver. The reticular system of the hepatic blood-vessels 

 corresponds to that of the symbiotic Spongoxenia, the system of the biliferous canals to 

 that of the canal-system proper of the sponge, the reticular framework of the hepatic 

 glandular cells to that of the maltha full of xenophya, and the supporting framework 

 of the hepatic connective tissue is comparable to that of the Keratose skeletal lamellae. 

 As in the case of the complex liver structure, the knowledge of the structure of 

 Cerelasma is only possible by means of sections through different planes. But the great 

 mass of foreign mineral bodies and siliceous particles crowded in the maltha makes it very 

 difficult to recognise the true structure of this remarkable Spongelid. 



The main mass of the body in Cerelasma is not formed by the horny framework of 

 the true skeleton, but by the xenophya, which are surrounded by thin horny envelopes, 

 and partly enclosed by the lamellae. These xenophya or foreign enclosures, which 

 compose the pseudo-skeleton, are in Cerelasma gyrosphsera (from Station 271) almost 



1 Cerelasma = Horny plate, Ktpx, t\a,zpa,. 



