310 SUMMARY OF CURRENT RESEARCHES RELATING TO 



cells that have undergone complete calcification. According to Koch 

 (1882), the skeleton is formed by extracellular secretion. According to 

 Krempf, each cellular area of the calicoblast layer functions like a gland 

 with merocrinal secretion, and the secreted material is elaborated 

 entirely within the cell. 



Developmental Stages in Rugose Corals.* — Thomas C. Brown 

 inquires whether there are only four primary septa in rugose corals, as 

 suggested by Kunth and until recently accepted by the majority of 

 workers, and recently shown by Gordon for Streptelasma frofandum, or 

 whether there are six primary septa, as suggested by Ludwig and the 

 Count de Pourtales, and claimed as definitely proved by Duerden. 



Brown has studied developmental stages in Streptelasma rectum Hall, 

 and he finds that in this species there is primary tetramerism. It is 

 probable that all the rugose corals are primarily tetrameral, and that the 

 appearance of six septa in the early stages of geologically late species is 

 due to the early development of the first pair of secondary septa. 



Primnoa reseda and its Embryos. f — J. Arthur Thomson describes 

 a fine specimen of Frimnoa reseda, the only species of its genus, from 

 the Faeroe Channel, 855 metres. It was almost a yard in height (34 

 inches), and its branches spread out for 16 inches. The colour of the 

 fresh colony, which soon faded, was a brilliant salmon-pink. In alluding 

 to this fact as new — for previous descriptions seemed to agree in describ- 

 ing the animal as white — the author overlooked the reference to this 

 species in Hickson's contribution to the Cambridge Natural History 

 (vol. i., p. 338), where the colour is described as " diffuse salmon-pink." 



Many of the colonies were crowded with diploblastic embryos, 

 spherical or ovoid in shape, from 0'l:-0"8 mm. in diameter or along the 

 longer axis. The ectoderm consisted of a single layer ; the endoderm 

 was a dense mass of cells. There was a large coelenteron and a very 

 marked middle lamella. 



New Genus of Pennatulids.| — Ch. Gravier describes Mesohelemnon 

 gracile g. et sp. u. in the family Kophobelemnonid®. It differs from 

 Kophohelemnon and Sclerohelemnon in the form of the spicules, in the 

 very short pinnules of the tentacles, and in the much smaller number of 

 siphonozooids, which are, however, individually well developed. The 

 spicules of the stalk are smooth two-headed rods, rounded at each end, 

 and sometimes drumstick like. The locality was the Gulf of Tadjourah, 

 on the coast of Somaliland. 



Pulsations in Jelly-fish.§ — A. G. Mayer has made some important 

 experiments. When the marginal sense-organs of the jelly-fish {Gassiopea) 

 are cut off, the disk is paralysed and does not pulsate in sea-water. But 

 if a ring-like cut, or a series of concentric broken ring-like cuts be 

 made through the muscular tissue of the sub-umbrella, the mutilated 

 disk responds to mechanical, electrical, or chemical stimulus, and 



* Amer. Journ. Sci., xxiii. (1907) pp. 277-84 (13 figs.), 

 t Proc. Roy. Phys. Soc. Edinburgh, xvii. (1907) pp. 65-72 (2 pis.), 

 t Comptes Rendus, cxliv. (1907) pp. 439-40. 



§ Carnegie Institution of Washington Publications, No. 47 (1906) pp. 1-62 

 (36 figs.). 



