ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 507 



verse fission ; it approaches Bougainvilliidae in having a single circlet of 

 filiform tentacles and a cylindrical hypostome not constricted off from 

 the body of the hydranth. 



The new genus may be defined as follows : — Hydvocaulus consisting 

 of long unbranched stems rising at short intervals from a small hori- 

 zontal hydrorhiza, the latter invested by a delicate annulated perisarc 

 continued on to the bases of the stems. 



Hydranths claviform, with a small number (commonly four or 

 five) of hollow filiform tentacles arranged in a circlet around the 

 thickest part of the body. 



Hypostome cylindrical, not constricted at its base. Asexual repro- 

 duction by budding and transverse fission. 



Medusa developed from the body of the hydranth ; when liberated, 

 globular with four unbranched radial canals and tentacles. Mouth simple. 

 Manubrium very short ; the stomach region provided with per-radial 

 pouches which in the adult are produced into finger-shaped diverticula 

 extending down the sub-umbrella. Gonads developed on the whole sur- 

 face of the stomach and its diverticula. 



It is likely that Mwrisia is a relic of the fauna of the Pliocene sea 

 which once covered the Fayuin depression. 



Porifera. 



Spicules of Leucosolenia.* — E. A. Minchin discusses the monaxon 

 spicules and describes their origin — each arising from a dermal 

 epithelial cell that divides into two, the " founder " and the "thickener." 

 The triradiate systems are then dealt with ; they arise from sextets of 

 cells, two of which give rise to each ray of the spicule. The gastral 

 rays and the derelict spicules in Leucosolenia complicata are then 

 discussed. Conspicuous rounded cells, full of coarse granules, arranged 

 in a superficial layer and in many cases appearing to be in process of 

 being cast off, are described as excretory. 



The author believes that the forms of monaxon spicules are not 

 explicable in terms of the physical properties of the material or as the 

 direct mechanical outcome of the conditions in which they develop. 

 The monaxon spicules owe the peculiarities of their form chiefly (perhaps 

 entirely) to their relations to the sponge-body, and are adapted to the 

 needs of the organism. But while the forms of primary spicules are 

 determined solely by their relation to the organism, and in no way by 

 their crystalline structure, when primary spicules are joined to form 

 secondary systems, crystallisation may be a condition determining the 

 angles at which they join. 



Encystation of Actinosphaerium at Different Temperatures.! — 

 Doris L. Mackinuon finds that at a low temperature, specimens of 

 Actinosphc&rium eichhorni form small and numerous cysts, with nuclei 

 scarcely below normal size, but markedly rich in chromatin. 



At a high temperature, the cysts formed are large and few in 



* Quart. Journ. Micr. Sci., Hi. (1908) pp. 301-55 (5 pis. and 5 figs.), 

 t Tom. cit., pp. 407-22 (1 pi. and 1 fig.). 



