ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 719 



of Crinoids vaiy among themselves leads to the hope that the details 

 of the tropical fauna may be elucidated by their aid. 



Similarly, according to Mr. Miers, the Crustacea collected have 

 one-third of their species widely distributed through the Indo-Pacific 

 region ; the affinity of the Australian with the European Amjjhipoda 

 is very remarkable, some of the species being identical. Mr. Miers 

 gives a very elaborate table of the distribution of the higher 

 Crustacea on the East Coast of Africa and the adjacent islands. 



Mr. S. 0. Eidley deals with the Alcyonaria and Spongiidfe ; of 

 the former there are 38 Melanesian species, and the author thinks 

 that few novelties are in the future to be expected from the shallow 

 water ; one-third of the Alcyonaria are new to science ; Psilacaharia 

 is a new genus of Melithteids, and its species is remarkable for the 

 large size of its spicules. Thirty -eight per cent, of the Melanesian 

 sponges are certainly new to science ; the greater number of novelties 

 belong to the Ceratosa ; as to individual variation, it is noted that 

 this often aflfects the size of the spicules ; variation in form of the 

 spicules is less common, that of external form is sometimes very 

 striking. Only a quarter of the species of sponges are known to 

 occur outside the Australian seas ; the most widely ranging are the 

 most generalized, but in some cases it is possible that the same specific 

 characters have been indei^endently acquired. Twenty-eight per cent. 

 of the sponges obtained in the Western Indian Ocean were found to 

 be identical with those of the Australian Seas. The most striking 

 point with regard to the sponges appears to be " the comparative 

 scarcity of forms showing marked distinctive characters of generic 

 importance which are not also found in the more familiar Atlantic 

 fauna." 



B. INVERTEBRATA. 



Origin of Fresh-water Faunae.* — Prof. W. J. Sollas points out 

 that the poverty of fresh-water faunte, as compared with marine, is 

 commonly attributed to a supposed inadaptability on the part of 

 marine organisms to existence in fresh water. That this is erroneous 

 is shown by the existence of fresh- water jelly-fish such as Limnocodium, 

 and still more directly by the experiments of Beudant, who succeeded 

 in accustoming several kinds of marine mollusca to a fresh-water 

 habitat. The view of Von Martens that the severity of a fresh- water 

 climate is prohibitive of the existence of most marine forms in rivers 

 is insufficient, and a more thorough-going explanation is necessary. 

 This is to be found in a study of the means by which the distribution 

 of marine animals is secured. 



In the case of stationary forms, free-swimming embryos are distri- 

 buted over wide areas by currents, and they can never pass from the sea 

 into rivers, in which the current is always directed seawards. Nor, 

 probably, could an attached form once introduced into a river perma- 

 nently establish itself so long as its projiagation took place exclusively 

 through free-swimming larvaj, for these would bo gradually borne 



* Nature, .\xx. (liJ84) p. Wd. 



