ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 73 



last year, and the searcli was rewarded by Mr. Bourne discovering on 

 some roots of Pontederia, imported from South America a few years 

 ago, a minute organism which proved to be hydroid in nature, and 

 obviously a phase in the life-history of the Medusa. 



Mr, F. A. Parsons, as noted infra (' Proceedings '), found the 

 organism in the previous April, though he was unable to identify it. 



Hydroid Zoophytes of the ' Willem Barents ' Expedition, 1881.* 

 — D'Arcy W. Thompson reports on the Hydroids collected during 

 the Arctic voyage of the ' Willem Barents.' The fact that there are 

 no new species is the natural result of the investigations of Sars, 

 AUman, Hincks, and others. Twenty-four species were collected, 

 some of which were hitherto rare. The most prominent and luxuriant 

 are Sertularia gigantea and Lafoea fruticosa, the former of which is 

 common in shallow, and the latter in deep water. Most of the species 

 are large and strong in comparison with specimens from further south. 

 Fifteen of the species are common in British seas ; two others present 

 well-marked varieties ; the rest have a very wide arctic or circumpolar 

 distribution. 



Structures liable to Variation in the Astrangiaoese (Madre- 

 poraria).t — S. O. Kidley's object in this paper is to show that what- 

 ever may be the value for classification of the corresponding parts 

 in the Turbinoliidae and Oculinidae, the columella, costas, and paliform 

 lobes must be employed with great caution in the study of the 

 Astrangiaceee. He describes two species of Phyllangia, which he 

 regards as " critical " — P. papuensis Studer and P. dispersa Verrill. 

 In the former he calls special attention to the variability of the 

 central columellar mass from a papillose to a trabecular type, and to 

 the variation in the source of gemmation, viz. from the stolon to the 

 sides of the calyces. In the latter to the variability of the costse, both 

 as regards actual and relative prominence and to the occurrence in 

 some individual corallites of some teeth on the margins of the largest 

 septa. 



Porifera. 



Development of Halisarca lobularis.| — W. J. Sollas finds that 

 the segmentation of the ovum of Halisarca is very irregular ; a 

 segmentation cavity is the exception, not the rule. The morula consists 

 of a large number of small cells imbedded in a structureless blastema. 

 The cells next begin to collect into irregular strings and heaps, forming 

 a rude kind of network. The singular mode of formation of the 

 gastrula is regarded as being due to the absence of a segmentation 

 cavity in the embryo, and may be considered as an " abbreviation " in 

 adaptation to development in a confined space. "The blastula is 

 not formed by the enlargement of a segmentation cavity, since this 

 otherwise empty space can be more advantageously occupied by cells 

 which subsequently became utilized in the formation of the gastrula." 

 The gastrula as well as the blastula stage is slurred over. 



The author suggests that the di\ergencies between his account and 

 that given by Metschnikoff, Barrels, and Schulze are primarily due to 



* Bijclr. tot de Dierkunde, Amsterdam, x. (1884) 10 pp. (1 pi.), 

 t Journ. Linn. Soc Lond. (Zool.), xvii. (1884) pp. 305-9 (1 pi.). 

 X Quart. Journ. Micr. Sci., xxiv. (1884) y>^. 603-21 (\ pi.}. 



