NATURAL HISTORY OF SLIPPER-LIMPET, 439 



The direct factor in the spread of Crepidiila, however, lies in con- 

 nection with the spawning habits, as may be gathered from what 

 follows. Crepidula spawns during the period from early March to 

 the beginning of November, but the greater number of individuals 

 appear to spawn about May. This limpet takes special care of its 

 spawn. It constructs about 50 to 60 membranous bags, into each 

 of which it passes about 250 eggs, and as the bags are made and filled 

 with eggs they are closed and fastened together by short cords. These 

 cords are finally all stuck on to the surface on which the slipper- 

 limpet happens to be sitting, so that when by taking away the spawn- 

 ing individual the spawn is uncovered, it looks like a bundle of 

 balloons, each containing a number of eggs. Each spawning individual, 

 therefore, lays about 13,000 eggs, which are carefully protected 

 beneath the shell of the mother until they are hatched. It is unlikely 

 that individuals would spawn more than once a year, but beyond the 

 fact that May seems to be a maximum spawning period, I have as yet 

 no definite information to offer. 



* To return to the fate of the eggs of Crepidula after they are laid : 

 the eggs are protected by the mother Crepidula for about a month, 

 but about the end of the month holes appear in the egg-bags, and the 

 developing Crepidulae escape by swimming away from their parent. 

 At this stage the Crepidulae resemble tiny shore sea-snails {Littorina), 

 having, however, a transparent shell. In this condition they swim 

 about at the surface of the sea, according to Prof. Conklin, for about 

 two weeks. Towards the end of that time the young limpets begin to 

 seek the bottom, and soon afterwards slipper-limpet spat having the 

 typical flat shell may be found on the various objects on the sea- 

 bottom. Thus young Crepidulae develop from the egg in about six or 

 seven weeks.f 



* The rapid spread of Crepidula along the Essex coast is now seen to 

 be easily possible, for young swimming forms could easily have been 

 carried by currents to the various parts of the coast, where they have 

 settled down and formed new centres for a wider distribution. It will 

 be an interesting problem to observe how far this species will spread in 

 the future. 



Besides the remarkable rate at which Crepidula is over-running the 

 oyster beds, the species presents another feature which the oyster 



* These paragraphs were inadvertently omitted from the original Report. 



t The information given of the development of Crepidula has been drawn largely from 

 Prof. Conklin's work ou Crepidula (see Journal of Morpliology , Vol. XIII, pp. 17, 18). By 

 observations similar to his I judge also that the period of develojjment from egg to spat is 

 about six or seven weeks. More definite information, however, is to be desired on this 

 point. 



