SCIENCE-GOSSIP. 



28? 



pose thai the first tentative efforts al Life occurred 

 in the shallow littoral region when' warmth, 

 shelter, and the action of the tides would greatly 

 favour both animal and vegetable growth. He 

 reminds us of the fad thai one very Lmportanl 

 group of marine animals, the Echinoderina, is 

 altogether absenl from fresh-water fauna; and 

 thai another large group, the Coelentera, is vev) 

 feebly represented. Only two classes have a pre- 

 ponderance in fresh water, the Amphibians (frogs, 

 newts, and the like), which arc altogether ter- 

 restrial or fresh-water in habitat, and Insects, 

 which, although not largely represented in fresh 

 water, are even more scarce in t lie sea. Protozoa, 

 however, as represented by Kadiolaria and Korami- 

 nifera, are almost exclusively marine, though 

 they are near relatives of Amoeba., which is 

 ubiquitous in fresh water. Foraminifera, though 

 abundant in estuaries and even in pools of marshes 

 where the water is only very slightly saline, 

 do not seem to he able to penetrate further than 

 this, and even in such localities they are invariably 

 depauperated, the tests becoming thin and de- 

 ficient in lime. Professor Brady adds the natural 

 reflection that it is possible that absence or di- 

 minished quantity of lime in the water may be a 

 chief cause of the absence of Foraminifera, just 

 as the sub-acidity and "softness " of the water of 

 peat-mosses seem to render it unfit to support 

 Microzoa with calcareous shells, while those with 

 merely chitinous valves are often abundant. 

 Sponges are almost wholly marine in their distri- 

 bution, of the forty odd families only one being 

 found in fresh water. Of the Coelentera (jelly- 

 fishes, zoophytes, etc.) only three families out of 

 about seventy are represented in fresh water, these 

 being the well-known Hydra and Cordylophora, 

 and two small and comparatively infrequent 

 Medusae. The heterogeneous group Vermes in- 

 cludes many fresh-water forms, but the larger and 

 more important section Arthropoda is very imper- 

 fectly represented. Of this division the micro- 

 scopic Entomostraca are the only crustaceans 

 found abundantly in fresh water, except the com- 

 mon crayfish ; the Spiders, on the other hand, are 

 absent from the sea, except the Mites and Pycno- 

 gons. Centipedes are wholly terrestrial, and 

 insects almost wholly so. The Mollusca are chiefly 

 marine, though some families are largely repre- 

 sented in fresh water. Of aquatic vertebrates, 

 fishes are, of course, the most important, and of 

 these, of 137 families, 35 only are found in fresh 

 water, and many of these but sparingly. The 

 Amphibians are, as already mentioned, entirely 

 absent from the sea. This is an interesting 

 epitome, and Professor Brady refers to a paper 

 published fourteen years ago by Professor Sollas 

 for the following principal causes why compara- 

 tively few animals have been able to establish 

 themselves in fresh water: — Firstly. the prevalence 

 among marine animals of larval forms so feeble as 

 to be unable to withstand river currents ; secondly. 

 prejudicial fluctuations of temperature in fresh 

 water ; thirdly, disturbing physical causes, such as 

 Hoods, droughts, upheavals and depressions of 



surface, etc.; and to this Professor lirady himself 

 adds the question of the non-salinity of fresh water. 

 In this connection he quotes the well-known ex- 

 ample of the transmutation of Irtemia salina into 

 .1. mulhaiiscnii, but this result lias been much criti- 

 cised and has recently been discredited. (See a note 

 in this journal, on p. 151 of the present volume.) 



Ross's New "Standard" Microscope. L'h< 

 popularitj of the Continental form of stand in out 

 hospital laboratories and medical schools, alluded 

 loon p. L84 in a recent notice of a new micro- 

 scope by Messrs. Peek, is further evidenced by 

 Messrs. Ross's latest stand, especially designed for 



this and similar classes of work. This stand has 

 iin usual Continental form of horseshoe toot, but 

 with the pillar broughl as far forward as possible 

 with a \ Lew to ob\ Lai Lng I he want of steadiness so 

 characteristic of this type of foot. The ■ 



adjust nt is the usual diagonal rack working at 



the end of the limb in a cylindrical slide, and the 

 other end of the limb, also in accordance with 

 Continental practice, is borne upon a triangular 

 bar and actuated by a direct -acting micrometer 

 screw. One drawback to this arrangement, what- 

 ever may be its advantages, is manifestly tha 

 whole weiirht of bodv-tube and limb is borne bv 



Ross's "Standard" Microscope. 



the fine adjustment, and that the limb the position 

 of which makes it peculiarly liable to strains and 

 ill-usage, is not rigid. Opinions, however, differ 

 on this as on other points connected with the 

 design of microscopes. The stage in the various 

 models varies in size from 3 inches to 1} Inches 

 square, and is covered with vulcanite. The sub- 

 stage in its simplest form is represented merely by 

 a ring beneath the stage, but in the more ex- 

 pensive stands by a rack and pinion sub-stage. 

 An iris diaphragm is fitted immediately beneath 

 the stage in the cheaper instruments, an arrange- 

 ment which, whilst effective with low power-, is 

 manifestly not advantageous when a condenser is 

 being used. The length of the tube is 160 milli- 

 metres, which in the larger stands extends to _.">i> 

 millimetres. The cheapest stand is priced at 

 £l 10s.. whilst the one illustrated costs with eve- 



