20 



further let me first give a brief resume of Kleinenberg's results so 

 far as they here concern us. 



In the first place, he records how the larval stomodoeum or 

 mouth is replaced in a very comphcated manner by the Annelid 

 permanent mouth or "Schlund". The latter is formed as a paired 

 involution of the stomodoeum, i. e. of the epiblast and this he con- 

 siders to have been originally stomodoeal glands. It encroaches upon 

 and swallows up the old mouth, and finally fusing with the hypoblast, 

 it opens into the intestine. 



The replacement of the larval mouth in Annelida by another 

 structure was already known, but Kleinenberg describes the steps 

 of the process in great detail, and he states that this mode of mouth 

 substitution by means of a paired involution is of very wide occurence, 

 in the Chaetopods. 



In it we have a direct parallel to the substitution of the old 

 Vertebrate mouth by means of a pair of gill-clefts, but, in truth, we 

 have something more. 



First as to some further processes in the development of the 

 permanent Annelidan mouth which seem to be of great importance. 



The paired involution also gives rise to the permanent mouth — 

 or "salivary" glands. 



Another phenomenon of extreme interest is the formation of the 

 special mouth or "Schlund" nervous system. This apparatus is only 

 concerned with the innervation of the permanent "Schlund" and 

 has no share in the innervation of the hypohlastic alimentary canal. 

 It arises as a special process of the hinder part of the suboesophageal 

 ganglion: this grows towards the developing "Schlund" becomes 

 closely attached to the latter, fuses with it, and gets pinched off from 

 the larger portion of the suboesophageal ganglion, which is left as 

 the first ganglion of the ventral chain. 



I must here digress in order to discuss the question of the 

 presence or absence of any representative of the supraoesophageal 

 ganglion of Annelids in Vertebrates,^) and here again Kleinenberg 

 comes to our assistance. 



I have myself devoted a good deal of attention to this point, 

 and have arrived at the conclusion (helds also I fancy, by Prof. 

 Dohrn) that there is no likelihood at all of our finding an area 

 in the Vertebrate brain which was ever pierced by the oesophagus, 



1) The consideration of Prof Sempeb's views on this point and on the 

 nature of the Vertebrate and Annelidan mouths I postpone. 



