SEA-FISHERIES LABORATORY. 



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The Nauplius and Cypris stages (figs. 10 and 11) of 

 Balanus halanoides, the common rock-barnacle at Port 

 Erin, are sometimes found in dense swarms — the former 

 in March and the latter about May. 



Fig. 10. — Nauplius stage of Balanx 



Fig. 11. — Cypris stage of Balanus. 



We have recently tried to determine the approxi- 

 mate number of nauplii set free in spring by the common 

 Balanus living between tide-marks. This can be done 

 by simply collecting barnacle-covered stones in March, 

 laying them exposed to air in the laboratory, and after the 

 lapse of a few hours separating the barnacles from the 

 stones with the point of a knife and placing them in a 

 vessel containing sea-water which has been kept in the 

 workroom for a day. Very soon after the detached 

 barnacles are placed in the sea-water it will be found that 

 the nauplii are hatching out and swimming towards the 



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