LATEE LARVAL DEVELOPMENT OF AMPHIOXUS. 225 



If, then, the club-shaped gland is shown to be a modified 

 gill-slit on the one hand, and is homologous with the intestine 

 of the Ascidians on the other, one is led to the apparently pre- 

 posterous conclusion that the intestine of Ascidians is the 

 morphological equivalent of a gill-slit. The secondary intes- 

 tine of Ascidians is certainly not homologous with the intestine 

 of Amphioxus. No other homology was thought of before 

 van Beneden and Julin suggested that of the club-shaped 

 gland of Amphioxus. My observations do not run counter to 

 that suggestion, except possibly in so far as they show that 

 the club-shaped gland is a modified gill-slit. The question is, 

 can it be both ? 



Reasons for regarding the Club-shaped Gland as a 

 Modified Gill-slit belonging to the Right Side — 

 the Corresponding Slit of the Left Side being re- 

 presented by the First Primary Slit. 



1. The club-shaped gland communicates with the exterior 

 at one end and with the alimentary canal at the other end. 



2. Its internal aperture, being dorsal to the larval endostyle, 

 is therefore to the right of the morphological middle line. 

 What was originally a simple branchial passage has thus been 

 virtually drawn out into a long tube, and the external aperture 

 has been shifted from the right to the left side. 



3. The first primary slit, being below the endostyle, is there- 

 fore to the left of the morphological middle line, and the 

 appearance which it presents of being distinctly behind the 

 gland is superficial and secondary. It lies in the region of the 

 second myotome. 



4. The club-shaped gland arises simultaneously with, and in 

 a similar manner to, the first primary slit, as a ventral pouch of 

 the alimentary canal (see Hatschek, 3) ; and though it arises 

 clearly in front of the first slit, this may be due partly to the 

 remarkable tubular form that it has attained as a result of its 

 evolution. I am not attempting to explain why it passes 

 across to open on the left side, but as it does so it must pass 



