170 REPORT OF COMMISSIOXERS OF IXLAND FISHERIES. 



If this be compared with the relative stages given in Table No. 5 

 (1904 group) it will be observed that the average length per stage for 

 the normal average of 1905 corresponds very closely with the normal 

 average of 1904, although it is less than the average size of the selected 

 normals for 1905. It is further evident, however, that the stage 

 periods of the 1905 group are, in general, greater. It is difficult to 

 assign a reason for this fact other than chance fluctuations in water 

 temperatures or the possible effects of light. It has always been ob- 

 served that the first four metamorphic changes in the young lobsters 

 follow each other in more rapid succession and that in consequence, the 

 individuals are larger and more healthy, when the temperature of the 

 water is near its maximum. It is during a few weeks in the middle 

 of the summer that all lobsters of whatever size experience their most 

 rapid growth.* 



On the other hand, as will ])e shown later, the effect of a strong 

 light may exert a harmful influence on the development of the young 

 lobsters. In the case of the group last mentioned (see Table No. 5, 

 also Nos. 23 and 24) lobsters were kept in open wire cages and not 

 protected from the sun's rays nearly as well as the lobsters which 

 were confined in the covered wooden cars, and whose records are 

 presented in brief in Tables Nos. 5 and 6 (1904 and 1905 groups). 

 The difference in the lengths of the stage periods will be readily 

 observed. A more detailed treatment of the influence of light upon 

 rate of development is undertaken on a later page. 



V. Possible Explanations of the Variations in the Rate of 

 Growth of Lobsters Mentioned in the Foregoing Tables. 



It is undoubtedly to such differences in the temperature of the 

 water that such a variation as is noticeable in the rate of growth of 

 the lobsters observed by Herrick at Woods Hole, and those of other 

 groups considered in Tables Nos. 5 and 6 is partly due. It is readily 

 noted that not only are the average first stage lobsters at Wickford 



*See Tables Nos. 18, 19, 20. and 21. 



