APPENDIX. 115 



one of them will appear clean and healthy while the other will be 

 covered with growths. In one a large percentage will survive, while 

 in the other the mortality will be high. The main cause will be the 

 difference in the current of water. 



By the angle of the paddle the amount of current is determined, 

 and the current determines the amount of food which is accessible 

 to the lobster, the extent of cannibalism, the ease with which they 

 molt, the amount of diatoms and other parasitic growths on the fry, 

 and those undeterminable factors which go to make up conditions 

 of health and vigor. 



That the proper amount of current should affect the accessibility 

 of the food, and to a certain extent prevent their eating one another, is 

 easily seen. That it should have an influence on the ease of molting 

 is also apparent. When the lobster molts it is, for a short time, more 

 or less helpless. A strong current throws it against the sides of the 

 box or forces it against the screenings. These conditions naturally 

 do not favor molting. On the other hand, if the current is very weak, 

 while it may be sufficient to keep an active larva moving, yet when 

 the molting period arrives the larva will sink to the bottom and be 

 rolled along with whatever food, silt, diatoms, and fungus spores have 

 collected there. The current must be so adjusted as to prevent both 

 of these difficulties. Why it should affect the parasitic growths on the 

 fry is not so easily seen. Because of the current continually running 

 in the boxes, a considerable number of diatoms, etc., will collect on 

 the inside of the box, and consequently there will be in the water 

 within the boxes. The number in the water within the boxes, how- 

 ever, cannot be much greater than in the water outside; at least not 

 enough greater to explain the abundant growths of diatoms which 

 sometimes occur. The probability is that the fry are infected with 

 these organisms by their contact with the sides of the boxes. With a 

 current great enough to continually throw the fry against the sides of 

 the boxes, the opportunity for their infection would be very great; 

 while with a current of less intensity the natural instinct of the fry 

 to shun any object would prevent this to a great extent. That this 



