1326 



AGRICUI.TURAI, MACHINERY AND IMPLEMENTS 



alternating currents set up between the sea and the lake should exercise a 

 differential excitation on the indi\dduals who have reached the stage of 

 readiness for migration. This migration therefore clearly bears a charac- 

 ter of tropism, as the immediate influence of the environment plan's a pre- 

 ponderating part. 



3) This tropism is chiefly of a respiratory kind, as the individuals, 

 whatever the direction of their movement, always pass from an environ- 

 ment poorer to one richer in dissolved oxygen. These conclusions are not 

 merely interesting with regard to the special case of the Mtigil. They also 

 bear on several other migratory fish, the journeys of which are longer and 

 more complex. It may be readily assumed as regards these latter that the 

 cause of the migration consists either in a reproductive instinct which forces 

 the genetic individuals tov/ards an environment necessary for the future 

 development of their spawn, or in an inherited memory which would call 

 these individuals back to the ancestral environment at the time of their 

 reproduction. None of these reasons of a psychic character and hypothe- 

 tical nature could be pleaded with regard to the Mugil, the migrations of 

 vv^hich, as has been seen, have for their principal cause a tropism of a respi- 

 ratory character. The writer, from the previous observations the series 

 of which he is now continuing, holds that this cause is likewise the one 

 governing the spawning migration of the Salmon. 



The method of biological investigation which seeks to establish the 

 curves of variation of the differential circumstances of environments in 

 problems of this kind, and to follow the variations in these curves in order 

 to determine those which constantly agree with the variable and successive 

 dispositions of the individuals is the only one which can produce rehable 

 results. These results are of two-fold importance, scientifically in respect 

 to the theory of migration, and practically with regard to fish breeding and 

 fisheries, provided that they are based on numerous and repeated observa- 

 tions so as progressively to eliminate with certainty all secondary circum- 

 stances of the character of mere coincidence. The writer therefore proposes 

 to continue these researches, and to undertake them on a larger scale, in 

 order to arrive at the most precise possible conclusions as to the deter- 

 mining causes of migration. 



FARM ENGINEERING. 



AGRICULTURAL 

 MACHINERY 



AND 

 IMPLKMKNX? 



1003 - Production of Agricultural Machinery in the United States in 1914. — Fann im- 

 plement News, Vol. XXXVII, No. 25, p. 13, i table. Chicago, June Z2, 1916. 



The Census Oftice of the Department of Commerce in the United States 

 has published a preliminary sunimary of the results of its enquiry into this 

 prodiiction in 1914, compared with igoo. 



Replies to the list of questions of the Deijartment were sent by 772 

 works which manufactured agricultural machinery in 1914, to an aggregate 

 value of $168 120 632. In 1909 returns, the corresponding figures had been 



