392 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the radial canals, give rise to the appearance of two streaks in each 

 of the main lobes, by the numerous spindle-shaped crystals which are 

 found in the terminal division of the ocular lobes, and by the large 

 size of the intermediate radial vessels. During growth the umbrellar 

 disk of the larva grows out of proportion to the eight lobes, new 

 structures appear on the buccal part of the oral tube, which seem to 

 be of great importance in the future rhizostomatous condition of the 

 animal. A closed annular canal is developed. Buccal tentacles 

 appear in the Cannostomous stage, and their early development may 

 be regarded as the " primary process superinducing rhizostomism " ; 

 this is then followed by the peculiar form of the four arms with their 

 extended distal margin, and these by paired, foldings of the brachial 

 processes. 



The chlorophyll-corpuscles already mentioned are regarded as 

 belonging to symbiotic algse, and the balls they form are thought 

 to be due to the continued division of a single cell ; they are present 

 in such quantities, that one is tempted to suppose that there is no 

 independent animal nourishment, but that the superfluous assimilation- 

 products of the alg£e are sufficient to support the medusae. After 

 long search, Claus has found Ehizostomata in an Ephyra-stage, but 

 he is anxious for smaller and younger specimens than those which 

 measure 3^ mm, 



Porifera. 



Calcisponges of the ' Challenger ' Expedition.* — This, the first 

 report on the ' Challenger ' representatives of any group of sponges, is 

 from the pen of a Eussian naturalist. Dr. N. Polejaeff. The Calcarea 

 were considered by Hackel as essentially littoral forms, and the fact 

 that two species were found by the ' Challenger ' at a greater depth 

 than 100 fathoms (viz. 450 fathoms, off the Azores), scarcely invali- 

 dates this conclusion, and at the same time accounts for the small 

 number of species (30, of which 23 are described as new) obtained by 

 the expedition. 



A great importance attaches to the report from the fact that the 

 author, having well-preserved materials and considerable time at his 

 disposal, and a good training in the subject, has devoted himself to 

 making the first thorough examination of the anatomy, and of the prin- 

 ciples of a natural classification, since Prof. Hackel brought out his 

 memorable work, the ' Kalkschwamme.' With regard to his prede- 

 cessor's results, he is led to the conclusion that, although Hackel's 

 "natural system" may be more natural than his "artificial" one, 

 it is still very far from absolute agreement with nature ; a con- 

 viction which has been more or less strongly felt by other observers. 

 He rejects Hackel's system of defining the genera solely by spicular 

 characters, pointing out that they are too variable for the purpose. 

 Considerable alteration is found necessary in Hackel's account of 

 the canal system. Thus, the assertion that inter-canals (the incurrent 

 canals leading from the pores) of the Sycones are wanting in a large 



* ' Report, &c., H.M.S. Challenger,' Zoology, xxiv. (1SS3) 76 pp. (9 pis.). 



