ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 227 



intermediary joints, and by the position of the nematotheca, close to,, 

 not at a distance from, the base of the hydrotheca. 



Northern Hydroids.* — Hjalmar Broch proposes to give detailed 

 diagnoses of all the species collected by the Ingolf Expedition, which 

 furnished copious material. The characteristics of the nutritive polyps 

 are of much greater systematic value than those of the gonophores or 

 the medusoids. An account is given of the minute structure of a 

 typical polyp, and then follows a key of athecate hydroids. The author 

 then gives an account of the Corynidse {Coryne), Myriothelidse {Myrio- 

 thela), Tubulariidse {Tubular ia, Corymorpha, Glava, Merona, Mono- 

 irachmm), BougainvilliidEC {Hydractinia, BougainvilUa, Perigonimus, 

 and Eudendrium). 



New Genus of Trachomedusae.t — H. M. Bigelow describes Eperetmus 

 typus g. et sp. n., from off southern Alaska. It is one of the Olindiidse, 

 with four metameres ; with primary tentacles only, and in a single series ; 

 with centripetal canals ; and with the otocyst capsules deeply imbedded in 

 and entirely enclosed by the gelatinous substance of the bell. 



Development of Alcyonium digitatum.| — Annie Matthews finds 

 that the fertilized ova of this common Alcyonarian segment in various 

 ways, but typical morulse always result. When the 16-cell stage again 

 divides to form the 32-celled embryo, delamination occurs, and the larva 

 becomes two-layered. The morula at the twentieth hour begins to 

 undergo a series of contortions, which last till the third day. This solid 

 contorted stage is termed the pre-planula, as it passes on into the hollow 

 planula stage. 



The pear-shaped planula, while swimming, exhibits characteristic 

 " planarian-like " movements, and on the fourth free-swimming day 

 (the seventh day of development) it settles down by the broad anterior 

 and aboral pole. 



The settled larva soon flattens, assuming a mound-like shape, and 

 on the second day of fixation eight mesenteries grow out simultaneously 

 into the coelenteron from the base of the lateral wall. The coelenteron 

 is identical with the hollow central space in the endoderm of the 

 planula. The mesenteries, arranged in four distinct pairs, grow 

 simultaneously and rapidly along the lateral walls and attached base, 

 and soon nearly meet on the basal and oral surfaces of the polyp. 

 Many round cells now appear at the base of columnar ectoderm. 

 Mesogloea is at this time secreted by the endoderm, and flows round 

 the above-mentioned ectoderm cells, cutting them off either singly or in 

 groups. These isolated ectoderm cells produce either nematocysts or 

 spicules, the spicules appearing soon after the mesenteries. 



Early on the third day eight simple hollow tentacles grow out, 

 alternating with the mesenteries, and encircling the oral surface. Later 

 on the third day the stomodaeum and mouth arise by the appearance of 

 a rapidly deepening invagination of the oral surface in the centre of 



* Danish Ingolf Expedition, v. (1916) No. 6, pp. 1-66 (2 pis. and 20 figs.). 



t Proc. U.S. Nat. Museum, xlviii. (1916) pp. 397-404 (1 pi.). 



i Quart. Journ. Micr. Sci., Ixii. (1916) pp. 43-94 (3 pis. and 51 figs.). 



