96 Journal of the Mitchell Society [August 



example taken April 30, 1923, which had 6 eggs and one nearly fully 

 developed larva in its brood pouch. The number of eggs or young 

 carried by an individual is quite variable, and, as will be noted later, 

 there is evidently a certain seasonal variation in the mean number of 

 eggs per brood. 



For the period during which these collections have been taken, 

 Mr. Hatsel has made sjDecial observations of temperature and specific 

 gravity of the water at the pier of the Beaufort Laboratory. As far 

 as practicable, records have been made twice daily, once at high tide 

 and once at low tide. I have grouped the records of temperature 

 for high and low water respectively, by five day periods and the ac- 

 companying table (p. 99) gives the maximum, the minimum, and the 

 mean for each unit period from May 20, 1922 to May 19, 1923. A pre- 

 cise correspondence is not found between temperature of water on 

 the one hand and cessation of breeding in fall and resumption in 

 spring. But, if temperature is the controlling factor, it is obvious 

 that gravid examples will be found for some time after the cessation 

 of breeding activities, and it may be expected that, after the temper- 

 ature in spring rises to a point favorable to the development of the 

 gonads, another period may elapse before breeding activities become 

 manifest in the discharge of eggs and filling of the brood pouches. 



Examination of the temperature records shows that prior to Nov- 

 ember 20, 1922, there had been occasional low readings of 14°C., al- 

 though the average for no five day period had fallen below 16°C. 

 There followed a sudden fall of temperature to a minimum of 10° 

 and an average for the next five day period of 13.4° (means of tem- 

 peratures at high and low water combined). Four immediately en- 

 suing five day periods (Nov. 26-Dec. 15) gave means of 9.4°, 10.6°, 

 14.1°, and 11.9°. Some gravid Limnoria were found up to December 

 12, but not later. As a matter of fact, eggs (without evident devel- 

 opment) were not found in any collection after October 26, at about 

 which time minimum temperatures of 14° C. first occurred, means for 

 a five day period being then at about 17°. 



During the remainder of the winter the averages for five day 

 periods varied from 11.3° to 5.7°, the lowest being in February. With 

 the first five days of March the mean rose from 7.6° in the last week 

 of February to 10.8°, and there was no subsequent serious slump. 

 Between ]March 11 and 15 there was a temporary rise to a maximum 

 of 17° and minimum of 14°, with a mean for the period of 15.4°. In 

 ensuing periods the temperatures were, of course, variable, but means 



