358 BULLETIN OP THE BUREAU OF FISHERIES. 



that while they tend to hold the body constantly with back to the light source they 

 may move up or down, back and forth; that is, toward or away from the source of the 

 stimulus, as a result of a variety of contending and conflicting influences, now one 

 winning the day, or the hour, now another. The issue may indeed vary from hour to 

 hour, and one might almost say from moment to moment. 



With the wonderful change registered at the beginning of the fourth stage, the 

 young lobster mounts to the surface and holds more persistently to it than ever before, 

 at times even jumping out of the water like a shrimp, though having discarded its larval 

 swimming organs and having brought into play the permanent swimmerets under the 

 tail. Every observer is agreed that of all the free-swimming stages the fourth is that 

 most commonly taken at the surface of the ocean, and especially in the brightest sun- 

 shine. This surface-swimming habit has further been observed by every experimenter 

 who has reared these young or turned them loose into the sea. At this point the experi- 

 mental testimony seems to conflict with the natural behavior of the lobsterling, since 

 during the early part of its fourth stage it has been observed to avoid the light. The 

 explanation would seem to be that this, like most of its similar reactions, is subject to 

 reversal, under conditions which are not as yet fully understood, but which, as Hadley 

 suggests, may be due to an increased intensity of the light stimulus or' to an impulse 

 which leads it to seek its food at the upper levels of the water. 



At the close of the fourth, or at some time probably near the end of the fifth period, 

 the little lobster makes its complete and final descent to lower regions. (Compare p. 348.) 

 Thereafter the bottom of the sea becomes its fixed abode, which it seldom or never leaves 

 unless snapped up by an enemy, or in after years it is hauled to the surface in a lobster pot. 



In the fifth and all later stages the light-shunning tendency becomes more and more 

 pronounced, but it can not be said that it is never subject to change, for more than 

 once I have seen adult lobsters exploring the bottom in shallow water on sunny days. 

 Yet their avoidance of strong light and their impulse to hide and to burrow after the 

 fifth stage is fairly constant. In a word, their behavior is no longer essentially vari- 

 able, but is in a measure stereotyped. 



VARIATION IN THE RATE OF GROWTH AND DURATION OF THE STAGE RERIODS. 



The following table shows the size and age of lobsters during the first eleven stages, 

 and is based upon data obtained at different points on the coast under different condi- 

 tions of temperature upon a varying number of individuals and by different observers. 

 New measurements of any number of individuals made under approximately similar 

 conditions would possibly give a different result, but this difference would not be great. 



I found that the fourth stage was reached at Woods Hole on the average in 14 

 days, while Mead has determined this period for Wickford, R. I., to be a'^little over 12 

 days, the average duration of the first three periods varying from 9 to 16 days, with an 

 individual variation of 3 to 7 days, according to the temperature and other conditions. 



Assuming that the lobster goes to the bottom to stay at the close of its fourth stage, 

 the pelagic life of the Woods Hole lobsters would be about 30 days, while at Wickford 



