318 J. H. OETON. 



In this group a special experiment has been tried with success, with 

 the object of entrapping young forms in a wire basket of a small mesh 

 inside which, as the animals grow, they become imprisoned. Food is 

 obtained by the animals from the natural growth on the wire basket and 

 the surrounding parts. The wire basket was placed in a large floating 

 wooden raft in Cawsand Bay adjacent to Plymouth Sound. From this 

 cage put out in the sea on the 28th May, 1913, and taken in on 26th 

 February, 1914, were obtained Palcemon senatus measuring on the 

 average about 5-6 cms. long from the tip of the rostrum to the end of the 

 tail, and two Portunus puber, one a male with a carapace width of 

 3-5 cms. and one female whose carapace measured 3-3 cms. wide. 

 As the greatest width of the mesh of the wire cage at the close of 

 the experiment was 14-5 mms., by 9 mms., it follows that the 

 specimens of Portunus were in all probability samples of the young 

 for the season of 1913, since the breeding season of this species of 

 Portunus falls in about the spring of the year. (See " Plymouth Marine 

 Invertebrate Fauna," p. 257, J.M.B.A., N.S., Vol. VII, No. 2, 1904.) 

 It is highly probable that the specimens of Palwmon senatus entrapped 

 in the cage were also examples of last year's crop of this species, and as 

 specimens about the size they attained occur in berry there would appear 

 to be little doubt that this species becomes mature and bears young 

 within a year. Some specimens are being kept alive in the tanks with a 

 view to watching their subsequent growth. 



An experiment conducted on similar lines on the Essex coast (see pp. 

 320 and 322) with a wire cage, the greatest width of any mesh of 

 which at the end of the experiment was less than 2 cms., yielded four 

 specimens of Carcinus mwnas, three males and one female. The width of 

 the carapace of the three males was respectively 3-6, 3-4, and 3-2 cms., and 

 that of the female 3-1 cms. This experiment extended over a period of 

 15 weeks between the 18th June and the 3rd October. Hence there 

 can be little doubt that the common crab also attains to maturity within 

 a year. Further experiments will be made with cages of wire having a 

 smaller mesh in the hope of following the rate of growth more fully in 

 these and other species of Crustaceai 



KATE OF GROWTH IN SOME MOLLUSCA. 



In the Mollusca group the age at which several species begin to breed 

 has been determined. The common mussel, Mytilus edulis, has been 

 found to spawn naturally at an age of one year. From eggs spawned in 

 this way a fertilization made by adding sperm from a male of the same 



