70 SUMMARY OF CURRENT RESEARCHES RELATING TO 



excretion of nitrogenous excreta seems to be effected by certain cells of 

 the vascular plexus. 



In conclusion, the genital organs are described ; in all the three 

 forms examined by the author, their structure was the same. In each 

 interradius there is a very large broad zone, concave outwards, in which 

 the subumbrellar gastric wall is particularly thin. These thin parts 

 grow so rapidly that they give rise to a large number of folds. On this 

 folded membrane there is a broad band in which the egg-cells are 

 formed and matured ; this band consists of three layers — a rather high 

 endodermal cylinder-epithelium, mesoglcea, and a low endodermal 

 pavement-epithelium. The young cells have neither membrane nor 

 follicle, though both appear later on. The male organs of Cramhessa 

 mosaica and Phyllorhiza punctata only differ from the female in that 

 sperm-sacs are developed in the place of eggs. 



Two new Types of Actiniaria.* — Dr. G. Herbert Fowler describes 

 two new Actiniarians found by the ' Challenger ' at Papeete. One, 

 which is called Thaumactis medusoides, is flattened and almost medusi- 

 form in shape, and is, perhaps, a free-swimming form ; as it is biconvex 

 it has no true body-wall, but the animal is divisible into oral and aboral 

 surfaces ; the former is beset by what the author calls pseudotentacles, 

 since they cannot be regarded as homologous with true tentacles in 

 number, position, or structure. In an expanded specimen fourteen true 

 tentacles surround the stomodseum. The pseudotentacles each arise as 

 a simple hollow outgrowth from the coelenteron ; the bud extends 

 laterally over the surface into three or four " roots," and is continued 

 upwards as a free, finger-like process ; the ectoderm on the apices of the 

 roots is generally well supplied with nematocysts, but no nematocysts 

 are found on the finger-like process ; these false tentacles have no rela- 

 tion to the mesenterial chambers, either in number or position. No 

 siphonoglyph could be recognized in the stomodseum. The musculature 

 of the general wall of the body is slightly developed, and consists of an 

 endodermal circular and an ectodermal longitudinal layer. Of the 

 twenty-one pairs of mesenteries found in the largest polyp, only one 

 pair are directive ; six are primary, and six secondary ; for the most 

 part the free edge bears the normal form of filament. 



The non-fixation and persistent biconvex shape of the polyp appears 

 to indicate a condition more or less ancestral, while, in the opinion of 

 Prof. E. Hertwig, the longitudinal muscle leads to a belief in a close 

 relation with the Hydrozoa. Its peculiarities may justify us in regard- 

 ing it as the type of a new tribe, the Thaumactinse. 



The other new form, which is called Phialactis neglecta, is chiefly 

 interesting from the fact that it affords another example of the retro- 

 gression of the tentacles; from the four genera already described by 

 Hertwig it differs in that the tentacles are not replaced by stomidia — 

 slight elevations of the oral disc, surrounding a large opening which is 

 homologous with the pore at the tip of some normal Actiniarian ten- 

 tacles — but by what Dr. Fowler terms sphseridia,"j" i. e. ampuUate diver- 

 ticula of the inter- or intramesenterial chambers, devoid of an opening 

 to the exterior, and homologous, therefore, with the imperforate tentacles 

 of many genera. 



* Quart. Journ. Micr. Sci,, xxix. (1888) pp. 143-52 (1 pi.). 



t It may be noted that Prof. Love'n has used the term " sphseridia " in a very 

 different sense. 



