1923] Breeding Habits of Limnoria at Beaufort, N. C. 97 



of approximately 14° or higher are found for all subsequent five day 

 periods except for the period March 31 to April 4, when, owing to a 

 sharp and very brief drop to a minimum of 8°, the mean was as low 

 as 11.9°. By April 14, when the mean temperature was about 16° 

 and the minimum above 14° for the first time since autumn, a very 

 substantial proportion of large Limnorias were gravid. As previous 

 collections in 1923, including one as late as April 3, showed no gravid 

 examples, and, as all eggs borne by the specimens taken April 14, 

 were apparently newly laid, it may be assumed that breeding began 

 rather suddenly on April 14 or within a few days prior thereto.'-. 



If, then, temperature is an effective factor m determining the lim- 

 its of the breeding season of Limnoria, the data in hand would fit 

 with the assumption that the production and deposition of eggs at 

 Beaufort, N. C, ceases when the minimum temperature in autumn 

 falls to about 14° C. and that the rise of temperature in spring stimu- 

 lates a renewal of breeding activity which is reflected in the filling of 

 brood pouches after the minimum temperature passes above 14°C. 

 The period during which no eggs or embryos were formed in the 

 brood pouches covered approximately four months (one-third of the 

 year) from about the middle of December to about the middle of 

 April. Of 29 collections made from May 1, 1922, to December 12, 

 1922, inclusive, only two included no gravid females and these were 

 made November 7 and 30. Of 11 collections made December 19, 1922, 

 to April 3, 1923, inclusive, none contained gravid Limnoria. 



As previously indicated, all eggs observed April 14 were appar- 

 ently new-laid. In 12 gravid examples taken April 21, several had 

 embryos showing substantial development, but only one had well 

 formed larvae. Of 38 gravid examples, an exceptionally large number, 

 taken April 30, more than one-fourth bore well advanced larvae and 

 about one-tenth were apparently fully developed. Of 10 examples 

 collected IMay 7, more than one-half bore fully developed larvae. 

 These results suggest that the incubation period, at this season of 

 minimum temperatures for breeding, is 2 weeks or a little longer. 



Breeding starts in spring with a real impetus. By April 30, prac- 

 tically all large females were gravid and in all the early collections 

 the brood pouches regularly contained large numbers of eggs or em- 

 bryos. In summer and fall pouches are often found to contain but 



^The first collection of 1922, made May 1, had a high iiroportion of gravid females, 

 including both eggs and advanced embryos. 



