LATER LAEVAL DEVELOPMENT OF AJIPHIOXUS. 223 



of the alimentary canal of Amphioxus at the time of the 

 forward extension of the notochord naturally rotated the 

 originally median ventral endostyle on to the right side in 

 company with the collateral organ^ now known as the club- 

 shaped gland. 



A comparison of the figures accompanying this paper, illus- 

 trating the development of the endostyle, shows clearly and 

 beyond question that everything dorsal to the endostyle is on 

 the right side of the morphological middle line, while every- 

 thing below it is on the morphological left side. Thus the 

 intra-buccal orifice of the club-shaped gland is on the right 

 side, and the first and succeeding primary slits are on the left 

 side — morphologically. At this juncture I want especially to 

 emphasise the relative positions of the intra-buccal orifice of 

 the gland and of the first primary slit. 



The oesophagus and stomach of the Ascidian, which arise, 

 ontogenetically, from the prsechordal vesicle, are practically un- 

 represented in Amphioxus — the part of the vesicle from which 

 they arise being suppressed. In fact, in their respective 

 capacities as oesophagus and stomach they are not even 

 theoretically present. Bearing this in mind, we can now pro- 

 ceed to compare the position of the club-shaped gland and its 

 apertures with the position of the intestine in the young 

 Ascidian. 



In the larva of Amphioxus the club-shaped gland is situated 

 behind the endostyle, i. e. at the posterior extremity of the 

 primitive prsechordal vesicle — in this respect agreeing with the 

 intestine of an Ascidian. In both cases the aperture of the 

 collateral diverticulum (whether gland or intestine) into the 

 alimentary canal is immediately to the right of the mid-ventral 

 line — in the one case actually, and in the other case morpho- 

 logically ; and in both cases the external aperture is on the 

 left side. The point of origin of the club-shaped gland between 

 the first and second myotomes also corresponds more or less 

 closely with that of the Ascidian intestine. There is, therefore, 

 a fairly strong case in favour of the homology of the two struc- 

 tures. The question still remains as to whether the club- 



VOL. XXXII, PART II. — NEW SEE. P 



