270 B. W. MACBRIDE. 



the tube-feet, consequent upon the loss of the locomotor 

 function, explains the reduced stone-canal and madreporite, 

 though probably their increased sensitiveness has helped in 

 developing the nervous system. 



Literature consulted. 



An account of the earliest publications on Echinoderm de- 

 velopment is not given here, since a resume of them will be 

 found in the papers I quote ; and I hold it to be a waste of 

 time to reiterate with each new paper the whole history of the 

 growth of our knowledge ab initio. I mention here only 

 those authors on whose results I have, so to speak, built, or from 

 whom I have found it necessary to differ. Ludwig's work on 

 the anatomy of Asterids (10) laid the foundation of our know- 

 ledge of the haemal and perihsemal systems ; though, as we have 

 seen, many of his ideas about these structures were incorrect. 

 Subsequently in treating of Ophiurids (11) he discovered the 

 genital rachis. Hamann (7) extended this result, and pointed 

 out the amoeboid nature of the primitive germ cells. Then we 

 had Ludwig^s great work on the development of Asterina 

 gibbosa (12), the first account of the metamorphosis of any 

 Echinoderm which had any pretence of completeness, and to 

 which I have constant occasion to refer. His account of the 

 changes in external form and of the development of the 

 calcareous plates can hardly be improved upon. Owing, 

 however, to the imperfect methods in vogue at that time he 

 failed to penetrate with equal success into the course of the 

 internal changes. He saw nothing of the segmentation of the 

 coelom or of the ring-like growth of the left coelomic vesicle ; 

 he saw nothing also of the origin of genital organs, ovoid 

 gland, or oral coelom. He did not observe the right hydrocoele 

 or find the origin of the perihsemal spaces. He missed the 

 fixed stage, and he does not seem to have had any clear con- 

 ception of the relation to each other of the larval and adult 

 planes of symmetry. We owe to him, however, the clear 

 distinction of pore-canal and stone-canal, and the recognition 

 of the fact that the pore-canal is completely independent of the 



