138 



products of the chase, and the establishment of temporary or permanent reserved tracts 

 within which the game may recuperate, have been the principal methods advocated 

 and adopted. These methods, however, affect only an insignificant part of the existing 

 species, and the absolute protection afforded to certain species often has led to harmful 

 results, as it interferes with the balance of nature. 



Opinion is moving more in the direction of the establishment in all suitable places 

 of absolute sanctuaries where no animals or plants of any kind are allowed to be killed 

 or taken, except for the direct advantage of the denizens of the sanctuaries, as for 

 instance by the removal of noxious individuals, the controlling of species that are in- 

 creasing beyond reason, and the extirpation of diseased and unhealthy individuals. 

 The national parks of the New World are examples on a large scale. In the United 

 States^ moreover, chiefly by private munificence, a chain of small sanctuaries suitable 

 for birds has been formed round the coasts. In Great Britain a new society was founded 

 in 1912 to educate public opinion and to endeavour to procure the 1'ormation of suitably 

 placed sanctuaries and to arrange for their permanent preservation. 



Marine Plankton. 



" Pulterism." The greater number of marine species (see E. B. xxi, 720 el seq.) are 

 carnivorous, and the ultimate source of the food supply of the sea, besides its theoretical 

 interest, may have an economic importance as bearing on the migration of pelagic fish. 

 It has been supposed generally that the basis of the food supply consisted of microscopic 

 plants, especially diatoms (E. B. viii, 169 et seq.}, which multiply in the presence of 

 sunlight, building up their protoplasm from inorganic constituents like the green vege- 

 tation of the land. These are devoured by larger creatures, which in turn are preyed 

 on by still larger animals. Professor Putter, of Bonn, partly as a deduction from 

 observations on the frequency of marine organisms, partly from examination of the con- 

 tents of their digestive organs, and to a lesser extent on experimental work, has ad- 

 vocated the view that a large number of marine animals can obtain their nourishment 

 directly from organic solutions present in sea- water, so living like many parasites in 

 a nutritive fluid, or like fungi. So far, however, this view has obtained few adherents. 



Artificial Rearing of Marine Larvae. E. J. Allen and E. W. Nelson, working at the 

 Marine Biological Laboratory at Plymouth since 1905, have been investigating the 

 methods of rearing the delicate pelagic larvae of marine animals. At an early stage 

 they found it necessary to try to grow cultures of diatoms which should be either 

 " pure," a result extremely difficult to obtain, or " persistent," by the latter term mean- 

 ing a culture which can be carried on practically indefinitely by inoculating fresh sup- 

 plies of sterilised water with the diatom required. Culture media, the basis of which 

 is either natural or artificial sea-water, had to be sterilised by heat or filtration, and all 

 the operations have to be conducted with bacteriological precautions. If normal sea- 

 water is the basis, the concentration of the nitrates, and probably also of the phosphates, 

 has to be increased, and some further modification, the exact nature of which the 

 authors have not yet discovered, has to be produced by treatment with peroxide of 

 hydrogen or with animal charcoal. Light and temperature are extremely important, 

 but the degree of salinity is indifferent within a wide range. 



They have succeeded in making a very large number of persistent cultures on these 

 lines. In the rearing of pelagic larval forms of marine animals, the young larvae are 

 placed in pure, sterile sea-water, along with a culture of a suitable diatom to serve as 

 food. As far as possible all other organisms are excluded from the vessels. To obtain 

 the larvae, pieces of ripe ovary are taken from a female with sterilised forceps and are 

 placed in sterile sea-water in a shallow glass dish, and then fertilised with active sperm 

 from a ripe male. In a few minutes the eggs are filtered through silk and placed in 

 larger vessels kept at a uniform temperature. In a few hours the healthy larvae rise to 

 the surface and can be placed in still larger vessels, where they are fed with the culture 

 found most suitable. The amount of food must be abundant from the first, but must 

 be prevented from getting too thick in the water, by shutting off some of the light or by 



