BECENT WOEK ON THE PROTOCHORDA. 243 



111 his remarks dealing with the larval mouth he attempts 

 to set aside my work on the later larval development alto- 

 gether; but he does not refer to a single figure of mine, so 

 that I do not know whether he doubts the accuracy of all of 

 them or only of some. 



During the transition from the lateral larval mouth to the 

 median adult velum the mouth maintains its integrity, but 

 alters its shape and rotates through an angle of 90°. 



Legros wastes pages of ink in denying this rotation, i.e. in 

 denying a self-evident fact. 



He goes on to say that the larval mouth does not, in its 

 entirety, become converted into the definitive mouth, but only 

 its anterior portion; the posterior portion closes up by fusion 

 of the lips ; and the evidence which he brings forward in sup- 

 port of this assertion is neither furnished by section nor by 

 direct observation, but by measuring the relative distance of 

 the posterior angle of the mouth from the tip of the snout. It 

 is quite true that this distance becomes somewhat shorter, 

 a fact which my figures and description render completely in- 

 telligible by the change of shape and position which the mouth 

 undergoes. No soldering of the lips whatever takes place, and 

 to assert that it does so on the evidence which Legros adduces 

 is mere trifling. 



The Ascidians naturally take up the most space in this 

 volume of the Traite, and the treatment which they receive on 

 the whole leaves little to be desired. In the account of bud- 

 ding in the Botryllidse the authors follow Pizon's work almost 

 entirely. On many points Pizon's results are in opposition to 

 the work of Hjort. It is a subject which requires more in- 

 vestigation. 



The volume concludes with a useful summary of facts and 

 of theories relating to the origin of the Vertebrata, from which 

 I will make one quotation only. On the subject of the prse- 



Atrial Chamber of Amphioxus," 'Quart. Journ. Micr. Sci.,' vol. 31, 1890, 

 where the external orifice of the club-shaped gland is figured both as seen in 

 to to and as seeu in section. 



VOL. 42, PART 2. NEW SERIES. R 



