344 Prof. E. W. MacBride. The Artificial Production of 



had already gone forth from them, aud that then, after the formation of these 

 organs on both sides had been determined, further nourishment became 

 available aud the left hydrocoele developed further, the structure of such 

 larvae can be explained. 



The second main result obtained by my experiments concerns the further 

 development of larvae which have been starved during the first week of their 

 existence. Such larvae have no hydrocoele — it is probable that that part of 

 the coelomic rudiment which should have developed into the hydroccele 

 becomes absorbed during the period of hunger. In the further history of 

 these starved larvae we see the potentialities of development of the Echinus 

 larva when the hydrocoele bud has been removed. It is, therefore, most 

 instructive to note that the power of forming pedicellarise has likewise 

 disappeared, and this result confirms the conclusion at which we had already 

 arrived, viz., that the power which determines the formation of pedicellarise 

 emanates from the hydrocoele. 



How are the extraordinary potentialities of the right side to be explained, 

 potentialities, it may be remarked, which are never called into activity during 

 the normal life of the species, and so far as we can judge have never been 

 utilized in the past history of the race ? We seem shut up to some such 

 hypothesis as this. When the Cefhalodisms-Yik.Q ancestor still possessed two 

 hydrocoeles, and whilst it was developing into a Proto-echinoderm with one 

 hydrocoele its dominant activities were comprised in the writhing grasping 

 movements of the tentacles which were the outgrowths of these hydrocceles. 

 These activities caused modifications to take place in the neighbouring tissues ; 

 and if one believes, as I do, in the inheritability of acquired characters, one 

 may assume that the tendency to produce these modifications was inherited, 

 so that the modifications were eventually evoked by the mere presence of 

 the hydrocoele bud before the activities of its lobes had begun. We must 

 further assume that the hormones which produced the modifications, tended 

 to be stored in the hydroccele bud itself — and that both hydrocoeles were 

 ultimately derived from the same small area of the coelomic wall. All the 

 hormones therefore necessary to produce the modifications which were 

 acquired after the Cephalodiscus-axLcestor by the loss of one hydrocoele had 

 become an Echinoderm, were still situated in the same place ; and so, when 

 this area under the influence of stimulation produced two hydrocoeles 

 instead of one, these hormones were shed abroad on both sides of the larva, 

 although they had only been evolved in connection with the left side. 



This hypothesis may help us a little way, but no one is more conscious 

 than I am how incomplete and unsatisfactory it is. We ask in vain what 

 sort of chemical composition we must ascribe to the right ectoderm and to 



