Bucephalus to the cockle. 61 



to a larval form was henceforth so easily traced. One objection 



to my hypothesis suggested itself, viz., the fact that many of the 



spheres seemed too small to be developing eggs. 12 But there is 



considerable variety in the size of the eggs of the Cockle whilst 



in the sacs, 13 and I have seen similar variety of size in the segmented 



eggs of the Oyster when discharged into the mantle for incubation. 



Moreover, there is an advanced stage in the Bucephalus in which 



the embryonic buddings of its limbs become almost invariably 



detached whilst in the tube, 14 owing partly to the struggles of the 



most advanced specimens, or to the rough usage sustained in 



their exit from the broken tube, and these portions appear to 



correspond thoroughly to the small spheres ;• the different stages 



of the creature being so often contemporaneous in one or other 



part of the tube, 15 that under any of the conditions my difficulty 



was met, and the objection vanished. 16 For several seasons I had 



offered rewards for Cockles in spawn, meaning thereby such as had 



eggs incubating in the mantle, as in the Oyster, on the supposition 



that the statements of the fishermen that they had seen them might 



be correct. But though very anxious to obtain the reward, the 



11 cocklers " never succeeded, and many now believe they were 



mistaken. 



Although I observed the co-existence of, I did not trace any 

 direct connection between, the ovisacs and the supposed uterine 

 tube, 17 yet it seemed possible that the latter might be either the 

 development or the prolongation of the tube into which the ovisacs 

 all led ; it appears impossible to disentangle the latter from the 

 former so as to trace either. Seeing, moreover, that when the 

 tube was present, it always exhibited, except when evidently just 

 emptied, 18 some stages of the same contents ; whilst no other 

 development of the ovisacs themselves, nor of the unsegmented 

 eggs in the ovary, either in the presence or the absence of the 

 tube, was ever traceable ; and when, lastly, the same eggs were 



12 February 18, 1873. April 29, 1873 (No. 3). Fig. H 1. 



13 April 14, 1873 (No. 2). May 20, 1873. July 9, 1873 (No. 2). March 5, 

 1874. Figs. E 1 to 5 ; F 1 to 3; G 1, 2. 



14 April 12, 1873 (No. 4). May 20, 1873. Figs. J 1 to 3. 



15 June 14, 1872. 



16 Since this paper was read, I have found a Cockle (April 29, 1875) in which 

 none of the spheres equalled in bulk the vitellus of the eggs then present in 

 the sacs, whilst the number of small spheres seemed so great, and they 

 appeared so situated in the tube, as to be incompatible with the theory of 

 detached members. 



» April 29, 1873 (No. 3). 

 18 April 16, 1873. Fig. C. 



