502 SUMMARY OF CURRENT RESEARCHES RELATING TO 



definite plan of cyclic sequence, producing a figure which is cyclically, 

 not bilaterally, symmetrical. Tentacles and sense-organs appear at 

 determinate points on the bell-margin. Histogenesis of tentacles and 

 sense-organs shows their homology. The origin of nematocysts from 

 the base of the ectodermal pad at the base of the tentacle is described. 

 Gonads arise as enlargements by proliferation of the ectodermal sub- 

 umbrellar epithelium of the radial canals. 



Hydroids of Pacific Coast of North America.* — H. B. Torrey 

 gives a table of distribution, a diagnostic key, and a systematic dis- 

 cussion of the hydroids of the Pacific coast of North America. He 

 also discusses in connection with a number of species the relation of 

 form and habit to surroundings, the development and regeneration of 

 tentacles, the problem of orientation, response to tactual stimulation, 

 the origin of branches and gonothecEe within hydrothecse, and the 

 occurrence of a Haleciid {Gampaleciwn medusiferum) with free medusa?. 



Peculiar Structure in Certain Hexacorallia.f — A. Krernpf finds 

 in 25-35 p.c. of individuals of Seriatopora, Stylophora, and Pmcilopora, 

 a peculiar structure — a solid strand, running along the ventral directive 

 mesenteries into the cavity of the body. Morphologically it is an in- 

 vaginated tentacle, about sixteen times larger than an ordinary tentacle, 

 and also modified in structure. But what its meaning is remains 

 obscure. 



Porifera. 



Studies on Hexactinellids.J — Isao Ijima in his third contribution 

 on this subject describes a new stalked Euplectellid of an interesting 

 structure, which he calls Placosoma paradictyum. Its most remarkable 

 feature is the massive development of the body and the differentiation 

 of a part of the external surface into an area, the frontal lattice, more 

 especially adapted to the reception and passing in of the water than 

 other parts of the same. 



In observations on the Euplectellidse generally, Ijima has tried to 

 improve the diagnosis. He makes it read : — " Lyssacine Hexastero- 

 phora of tubular, cup-like or massive body ; sometimes stalked ; either 

 rooted by a tuft of basal spicules or firmly attached by compact base ; 

 generally possessing numerous separate oscula. Dermal skeleton com- 

 posed of hexactinic dermalia, the proximal ray of which is as a rule 

 much longer than any other in the same spicule ; no hypodermal 

 pentactins ; hexasters various." 



The present contribution also contains descriptions of Leucopsacus 

 orthodocus Ij., L. scoliodocus Ij., Ghaunoplectella cavernosa Ij., G. spini- 

 fera sp. n., Gaulophacus rotifolium sp. n., and SympageUa anomala sp. n. 

 These are referred to two families — Leucopsacida? and Caulophacidge 

 — newly conceived and proposed for introduction into the system. 



Note on Spongilla fragilis.§ — R. von Lendenfeld took specimens 

 of this fresh-water sponge from the Moldau at Prag and placed them 



* Publications Univ. California (Zool.), i. (1902) pp. 1-104 (11 pis), 

 t Coniptes Rendus, cxxxvi. (1903) pp. 1210-2. 



X Journ. Coll. Sci. Imp. Univ. Tokyo, xviii. (1903) pp. 1-124 (S pis.). 

 § Arch. f. Naturges., 69th year, vol. i. (1903) pp. 181-2 (1 pi.). 



