470 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



The astral fibrillse do not therefore arise merely through the re- 

 arrangement of a pre-existing alveolar structure (Biitschli, Eismond, 

 Erlanger) or reticulum (van Beneden, Hertwig, Kostanecki), but are 

 progressively differentiated out of the substance of the alveolar walls. 

 Wilson's results are in harmony with the view advocated by Kolliker, 

 Unna, Rhumbler, and many others, that an alveolar may readily pass over 

 into a reticular or fibrillar structure, and that neither of these types of 

 structure can be regarded as of universal occurrence or fundamental 

 significance, or even as constant in the same cell. 



The granules or microsomes imbedded in the meshwork are not 

 coagulation products, but pre-exist in the living substance. There is 

 ground for the conclusion that while the microsomes and alveoli differ 

 both chemically and physically, both are liquid drops, and have the same 

 origin in an apparently homogeneous basis or matrix, and that micro- 

 somes themselves graduate down to the smallest visible " granules." 

 Thus the view is again suggested that the matrix itself, in which all 

 these bodies lie, is composed of still smaller elements, by the enlarge- 

 ment and transformation of which the visible elements arise. 



Ccelentera. 



Zoophytes. * — Prof. S. J. Hickson took this for the subject of a 

 presidential address to the Manchester Microscopical Society. From 

 among his interesting remarks we select two: — "I have examined a 

 very large number of specimens of Millepora from the East Indies, 

 Indian Ocean, and West Indies, from the exposed reefs, to the depth of 

 30 feet, and have not yet found a single specimen in which the super- 

 ficial canals were not crowded with Zooxanthellaj.'' It seems to be an 

 essential symbiosis. 



In some cases the surface of Millepora is almost covered with little 

 key-hole apertures, through which the appendages of the barnacle Pyr- 

 goma milleporse project. If tlie crustacean dies, the tissues of the ccenen- 

 chym cover over the aperture, and the shell is buried. But the effects 

 of the gall-like growth do not all at once vanish ; the locality projects 

 from the surface as a little tubercle for some time afterwards. These 

 warted forms, which occur only in shallow water, have been called 

 M. verrucosa ; but this is absurd, for it is only the accident of the shallow 

 water habitat that makes a millepore " verrucosa." 



Sense-Organs of Deep-sea Medusse.f — Dr. E. Vanhoffen finds that 

 the medusae of the German Deep-sea Expedition include species of 

 Periphylla, of Atolla, and of a new genus, Periphyllopsis. All three 

 genera are clearly of deep-sea habitat, and were sufficiently well preserved 

 to allow of an examination of the sense-organs. These prove to be sim- 

 pler than was supposed by Haeckel and Maas, no trace of ocelli being 

 present. In Periphylla the rhopalia consist of a canal clothed in pig- 

 mented endoderm and protected by well-developed mesoglcea. Over the 

 otoliths the canal becomes somewhat widened, and this produces an ex- 

 ternal swelling, further emphasised by a thick sensory cushion which 

 surrounds the rhopalium on its under side. The rhopalia of Atolla are 

 generally similar to those of Periphylla, but the sensory cushion has at 

 either side a large ganglion, which the author regards as probably the 



* Trans. Manchester Micr. Soc, 1899, pp. 26-35. 

 t Zool. Anzeig., xxiii. (1900) pp. 277-9. 



