ON THE LIFE-HISTORY OF PEDICELLINA. 251 



for fixation), but also that ectodermic thickenings, the com- 

 mencements of the buds, are to be detected some time before 

 the embryo is ready to leave the maternal vestibule, the possi- 

 bility of the development having been influenced by abnormal 

 conditions being here out of the question. 



In figs. 17, 18, and 19, the position of the dorsal organ is 

 represented as not having been much altered during the rota- 

 tion of the alimentary canal, which has, so to speak, been 

 pulled through the loop formed by the dorsal organ and the 

 somewhat hypothetical suboesophageal ganglion. Assuming for 

 the moment this position for the dorsal organ, we find that 

 throughout the metamorphosis the buds retain their original 

 situation (in Loxosoma) between the dorsal organ and the 

 ciliated ring, and that their position with regard to the oeso- 

 phagus is practically the same as that which characterised them 

 at their first appearance. 



Is there, however, any reason for believing that the position 

 of the dorsal organ is correctly indicated in the diagrams ? It 

 seems to me that this question must be answered in the afiirma- 

 tive. In the first place, the degenerating dorsal organ of 

 Pedicellina does in reality occupy this position, and in the 

 second place {vide No. 3 of Barrois' conclusions on p. 248), 

 the circumoesophageal commissures may be represented by the 

 strong ganglionated nerves passing from the ganglion to the 

 ''posterior sense-organs" in L. crassicauda, as originally 

 described by Salensky (see also No. 4, PL xix, fig. 1). Should 

 the metamorphosis of Loxosoma be proved to bear out this 

 suggestion of Barrois', we must assume either that the whole 

 brain has atrophied, or that the adult possesses at most a small 

 portion of the brain at the ends of the two widely separated 

 oesophageal commissures. 



With regard to the actual metamorphosis of Pedicellina, 

 I have to point out that I have not succeeded in demonstrating 

 the presence either of oesophageal commissures or of a sub- 

 oesophageal ganglion. The latter structure becomes distinct 

 only at a stage later than fig. 10, and it then has the positiou 

 which characterises the adult ganglion. 



VOL. XXVII, PART 2. NEW SEH 8 



