282 SUMMARY OF CURRENT RESEARCHES RP2LATING TO 



inwards; on each side of the ventral mesenteries is a single mesentery, 

 with its longitudinal muscle facing the outwardly-directed muscle of the 

 corresponding directive mesentery, so that at first sight there appears 

 to be only one pair of directive mesenteries. The mesenteries of the 

 sixth pair are very slightly developed, are without filaments, muscles, 

 or gonads, and are placed in the ventro-lateral spaces. 



Nervous System of Lucernaridae.* — N. Kassianow has studied this 

 especially in Craterolophus tethys and Lucernaria campanulata, and finds 

 that it consists in the first place of a nerve-plexus in the exumbrellar 

 ectoderm which extends over the whole external surface. There are 

 also nerve-centres belonging to the sub-umbrellar ectoderm wbich lie 

 at the tips of the arms, the nervous epithelium spreading between the 

 bases of the tentacles. In Craterolophus tethys there are also ganglion- 

 cells and nerve-threads in the musculature of tentacle-stalks, while in 

 Lucernaria the marginal muscle and the longitudinal muscles contain 

 nerve-threads and probably also ganglion-cells, and there are also nerve- 

 threads in the stinging epithelium of the sub-umbrella. In Cratero- 

 lophus there are sensory cells in the ectoderm of the margin where this 

 borders the bases of the arms. In both forms and also in Haliclystus 

 octoradiatus there is a layer of nerve-threads, of ganglion-cells, and of 

 special sensory cells in the knobs of the tentacles, and nerve-centres 

 consisting of sensory epithelium belonging to the batteries of stinging- 

 cells, and arranged round the openings of these. In Craterolophus tethys 

 there are also nervous elements in the stinging knobs of the marginal 

 papillae just as in the tentacle knobs, and similar nerve epithelium 

 occurs in Haliclystus at the base of the marginal papillae. In Lucernaria 

 scattered ganglion-cells and sensory cells occur in the endoderm of the 

 gastric cavity. The author does not believe that the arms of Lucernaria 

 can be homologised with the sensory lobes of Discomedusae, nor the 

 nervous system of the former with that of the other Scyphomedusaa. 

 The nervous system of the Lucernaridae is simpler than that of the 

 other Scyphoniedusae, and has developed along parallel lines but in- 

 dependently. It does not however show any relation to that of the 

 Hydromedusae. 



Plumularidae.f — Prof. C. C. Nutting has completed a fine monograph 

 on the North American representatives of this family. The minute 

 structure of the trophosome and the gonosome is discussed in detail ; the 

 oogenesis, spermatogenesis, and development are likewise described ; a 

 special section is devoted to the stoloniferous multiplication ; and the 

 interesting question of the possibility of conjugation is discussed in a 

 fair-minded manner. Then follows the systematic discussion. We 

 cannot pretend to summarise a large monograph, but it impresses us as 

 a, thorough piece of work, and an admirable achievement. 



Porifera. 



Ephydatia blembingia.ij: — Richard Evans describes this new fresh- 

 water sponge, one of the Meyeninae, found in a deeply shaded pool in 

 the Siamese Malay States. 



* Zeitschr. wiss. Zool., lxvi. (1901) pp. 287-377 (4 pis. and 11 figs.). 

 t Smithsonian Inst, Special Bulletin, 1900, 142 pp. 34 pis., 121 figs. 

 j Quart. Jouin. Micr. Sci., xliv. (1900) pp. 71-109 (4 pis.). 



