On the supposed Vertebration of the Tail in Appendicularia. 297 



groups. We are almost forced to this conclusion by the absence of 

 proof or even of probality of degeneration in these forms. 



The absence of vertebration, however (we are at least justified 

 in saying that vertebration has not been proved), may not of itself be 

 sufticient reason for concluding that these animals ought -to be ex- 

 cluded from the vertebrate i)hylum. Bateson *) has pointed out that 

 a considerable api>roach to segmentation may be found in a group of 

 unsegmented animals , as, for example, in Gunda seqmentata among 

 the Platodes. Therefore he is of opinion that segmentation may arise 

 within an unsegmented group; it is apparently not necessary to sup- 

 ])ose that it has been inherited. 



To sum up, then, segmentation is absent in the axial chord; it 

 is absent in the nerve cord equally in the body and in the tail; and, 

 from the foregoing observations, we cannot hold that segmentation is 

 present in the musculature. Even if it could be held that the structure 

 of the musculature of the tail implied true metamerism, the discrep- 

 ancy which Seeliger, as already stated, first pointed out between 

 the number of the so-called ganglia of the caudal nerve and the 

 number of the "muscle segments" would quite prevent the application 

 of the term to the tail as a whole. 



Since the completion of the above paper the supplement to the 

 third volume of Buonn's "Classen u. Ordnungen d. Thierreichs" has 

 come into my hands. In fig. 5, tab. 4 of that work the nuclei of 

 tin; muscles are represented with a regularity which I have never found. 

 Nor have I seen the corjjuscles on the nerve filament of F. furcata 

 with the structure shown in fig. 9, tab. 3. 



In conclusion I have to thank Professor Young for valuable help 

 in the preparation of this paper. It may be mentioned that Dr. 

 Young for many years has taught, that the structure of the tail of 

 Appendicularia was quite devoid of any metameric significance. 



Since the above was placed in the printer's hands my attention 

 has l)een directed to two further papers on this subject. 



In the earlier of these Lefevre *) states as the result of his 



1) Bateson, On the ancestry of the Chordata, in: Quart. Journ. 

 Microsc. Sc, (N. S.) V. 26, 1886. , 



2) G. Lefevbe, in: Johns Hopkins Univ. Circ, V. 13, No. Ill, 

 April 1894. 



