REPORT ON THE ASTEROIDEA. 187 



spreading a little way along the arms and on the dorsal surface of the disk ; the young 

 escape from the marsupium chiefly in the neighbourhood of the angles between the 

 rays." 



" We took A rchaster excavatus only on that one occasion; and the weather was so 

 boisterous at the time that it was impossible to trace the early stages in the development 

 of the embryo. * It is evident that the process generally resembles that described by Pro- 

 fessor Sars in Pteraster militaris ; and it is quite possible that, while th re is certainly 

 not the least approach to the formation of a locomotive bipinnaria, as in that species some 

 provisional organs may exist [at] an early period." 



The specimen upon which these observations were made has been figured in PI. 

 XXXI., a number of young in different stages of development are admirably preserved 

 in situ, and may be seen protruding from amongst the paxillse in- the intei brachial 

 regions. As noticed by Sir Wyville Thomson, it is in all cases the actinal surface which 

 is first presented, and even whilst the young starfish is still resting entirely within the 

 arcade-like spaces amongst the paxillse and before any protrusion of the rays takes place, 

 this appears to be the normal posture, i.e., the actinal surface uppermost. 



From the remarks above quoted it would appear that Sir Wyville Thomson was under 

 the impression that the young were even at this stage actually attached to the parent by 

 the centre of the abactinal surface, although he was unable to satisfy himself by what means 

 this was effected. Like him I have failed to detect any organic or membranous connec- 

 tion, and I am disposed to think that such did not exist. I make the remark, however, 

 with all reserve and caution, for it would obviously be bold to dogmatise on the former 

 existence of such a delicate connection, of which no trace remains after the specimen has 

 been preserved in spirits for so long a time. I may further remark that not the slightest 

 trace of any extension or projection of any of the larval tissues can be detected ( n the 

 dorsum of a young individual of about 3 mm. in diameter, which I have reduced to serial 

 sections. The paxillse of the abactinal surface are fully formed, and the epidermal or 

 dorsal membrane, which covers the plates from which the paxillse spring, is continuous. 

 The mouth also is fully formed, and the oesophageal portion of the alimentary tract is 

 capable of considerable protrusion. 



The form of the young individual is remarkable. The height is nearly as great as the 

 total diameter ; the abactinal surface forms a subplaue area excepting the slight round- 

 ing or convexity along the median radial lines, whilst the actinal surface is prominently 

 convex, with the mouth at the summit of the curvature, which slopes thence at a rapid 

 angle of declivity to the extremity of the rays. 



The largest young one carried by the starfish under notice measures about R = 3'5 

 mm., and has ten or eleven pairs of tube-feet in each ray. There are four or five spine- 

 lets on each adambulacral plate, one prominent into the furrow, the others forming oblique 

 pairs behind it, though some may stand singly. The transverse disposition of the groups 



