238 Period of Shrimps' Egg-hatching. 



Herdman records* that on the Lancashire coast, in December 

 and February, " most of the shrimps examined had spawn." In 

 March there were 60 per cent., in April 75 per cent, to 85 per 

 cent., and in May 60 per cent, to 80 per cent. Furthermore, 

 he observes, in said neighbourhood there seems to be two chief 

 spawning periods in the year November, and April and May. 

 He remarks that Ehrenbaum has found the same thing on the 

 German coast.f All we can say, from old shrimpers' expe- 

 rience and our observations, is that in the Kent and Essex 

 District these conditions do not obtain. Irrespective of 

 varying monthly and annual per centages of spawners, or 

 defective observations, or errors of method or calculations, 

 certain broad facts remain regarding the Brown Shrimp. 

 They are that March, April, May, sometimes June, are the 

 maximum months when the eggs fully ripen and hatch out ; 

 October and November the minimum. Further, that every 

 day of the year a few or many are to be found in a berried 

 condition. We are thus led to inquire, what length of time 

 does it take to hatch out the eggs carried on the abdomen 

 of each shrimp ? and are the eggs shed all at once or by 

 degrees ? We are not prepared to give decisive answers 

 to these queries. J From what occurs in other Crustacea 

 the lobster, the edible and the shore crab, for example there 

 is every reason to believe that the Common Shrimp likewise 

 carries its spawn for several months, and that the eggs ripen 

 gradually, or, so to say, do not all liberate their embryo-brood 

 at one sharp effort. This applies more particularly to the 

 big, old female Brown Shrimps with large numbers of 



* In Lane. Sea-Fish Labor. Reports for 1892 and 1894; also Trans. Livpl. Biol. Soc. 

 4th Ann. Rep.. 1890. 



t On this head we find Ehrenbaum in his memoir does enunciate two maximum 

 periods mid April to beginning of June and October and November. Howsoever, 

 from his tabular data and context, we are inclined to take a modified view of the case. 

 Egg-bearing in shrimps (both Crangon and Pandalus) does not necessarily mean 

 immediate expulsion of embryo from the egg. Temperature is an important factor 

 in advancing or retarding incubation, as Ehrenbaum himself accentuates : and even 

 age of animal influences an early or later breeding tendency. Within the Thames area 

 the autumn months seem those of sexual congress, this being accelerated or delayed 

 according to nature of season and concomitant circumstances. The October and 

 November egg-bearers are only the forward product. Moreover, too much stress must 

 not be laid on per centage numbers in spawn, for the reasons given above. 



J Ehrenbaum says that in the summer time in his aquarium eggs hatched in four 

 to five weeks, though in winter he believes they take as many months to ripen. 



