914 REPORT— 1898. 



which, we venture to think, is likely to prove of some value in cognate researches, 

 some of which we hope subsequently to undertake. 



The experiments have entailed some considerable expense, and to continue the 

 ■\vork a duplicate apparatus is necessary. We therefore venture to apply to the 

 General Committee of the British Association for a grant of 15/. in aid of this 

 research. 



TUESDAY, SEPTEMBER 13. 

 The following Papers and Eeports were read : — 



1. On Musical Organs in Sjnders. By R. I. PococK. 



2. On the Origin of the Vertebrate Notochord and Pharyngeal Clefts. 

 By A. T. Masterman, B.A., D.Sc. 



The three leading anatomical features of the Chordata are usually represented 

 to be the dorsal nervous system, the notochord, and the pharyngeal clefts. Of 

 these the first does not stand out so distinctly as do the others, because in the great 

 majority of the invertebrate phyla there is found a certain important portion of 

 the nervous system, i.e. the supra-cesophageal ganglion, which has a dorsal position 

 relative to the orut. 



The other features are not in any way characteristic of other T)hyla, and are 

 conspicuous alike in their morphological and ontogenetic features. 



Morphologically the notochord and the pharyngeal clefts have little in common. 

 Both are absent in the adult Amniota, and both take a more prominent part in 

 the constitution of the lower vertebrates than that of the higher. 



Ontogenetically they both arise from the same layer, i.e. the hypoblast, and 

 first appear as local hypertrophies of the alimentary canal, taking the form of 

 diverticular outgrowths, which differ in that whilst the notochord, in the higher 

 forms, becomes completely separated from the parent layer, the pharyngeal pouches 

 come into contact with the epiblast, and eventually (in most) acquire an opening 

 to the exterior. The inference from these morphological characters is that both 

 the notochord and pharyngeal clefts have in the early history of the vertebrate 

 animals played a far more prominent part in their structure than at present. 



In the case of the notochord, those of the true Chordata, in which it does not 

 disappear in the adult, seem to make use of this organ as an elastic axile support 

 intimately connected with the myomeric muscles and the mode of locomotion 

 adopted by the aquatic chordates. 



At the same time a little consideration will lead us to believe that the assump- 

 tion that this is the primary function of the notochord will in no way explain the 

 facts either of morphology or of ontogeny. 



In the ontogeny of the notochord it is clearly derived, as already stated, from 

 the hypoblast, and only secondarily in the process of development does it move 

 away from its parent layer and take up a median axial position for the supporting 

 function. No theory yet suggested takes sufficient account of this peculiar origin, 

 which is unique for organs of sujoport. 



The legitimate inference is that the primary function of the notochord was 

 directly connected with the endoderm and, in all probability, with the function of 

 alimentation. 



The morphology of Amp/no.iits and that of the Tunicata sheds no further light 

 on the question, but there are certain forms which, mainly for the reasons here 

 referred to, may be placed together in one crroup, Archi-chorda, which present in 

 their adult anatomy various conditions of the notochord which correspond to the 

 ontogenetic stages of the same organ in the higher Chordata. 



Thus in Balanoglossus, Cephalodiscus, and larval Phoi-onis certain parts of the 



