222 ARTHUR WILLET. 



before the atrophy of the subchordal portion of the intestine, 

 had an anus at the posterior extremity, as is the case with 

 Amphioxus. This primitive outlet has, therefore, been sup- 

 planted by the development of the outgrowth from the stomach 

 mentioned above, which van Beneden and Julin call a collateral 

 diverticulum, and at the same time make the suggestion, 

 which ray observations tend to support, that the intestine of 

 the Ascidian, arising as above described, is homologous with 

 the club-shaped gland of Amphioxus. 



The Endostyle and Club-shaped Gland of Amphioxus. 



We must now define the position of the endostyle in the 

 larva of Amphioxus in order to grasp the situation of the club- 

 shaped gland. 



It has been already implied that in all probability the 

 ancestor of Amphioxus was provided with a praechordal region 

 and was symmetrical; and, in fact, resembled an Ascidian tad- 

 pole before the atrophy of the subchordal portion of the 

 intestine. 



In the larva of Amphioxus the endostyle lies at the extreme 

 front end of the alimentary canal, which, as we have said 

 above, represents the median portion of the anterior or ' prse- 

 chordal ' chamber, the lateral portions of which formed the 

 anterior intestinal diverticula. It is further placed in the 

 region of the first myotome ; its peculiar oblique and lateral 

 position has been already dwelt upon and explained. It also 

 lies immediately in front of the club-shaped gland. 



It results, first, from the analogy of the Ascidian tadpole, 

 and secondly, from the position of the endostyle in the larva of 

 Amphioxus, that it (the endostyle) was originally differentiated 

 as a mid-ventral groove in the prsechordal region. This primi- 

 tive anterior position for the endostyle had been previously 

 surmised by van Beneden and Julin, so that my account of 

 its development in Amphioxus harmonises well with their con- 

 clusions. 



The transverse growth which affected the anterior region 



