BY .IAS. P. IIILL. 21 



anterior to the internal openings of the collar canals, two distinct 

 spaces exist. 



With regard to the division of the collar coelom into two halves, 

 considerable variation exists in this species. Dorsal and ventral 

 septa may be entirely absent, the two side halves of the ccelom 

 then standing, as in Balanoglossus kiijjfferi according to Spengel, 

 in open communication. 



The dorsal septum when present differs from the normal 

 condition in Ft. minuta\\'\th regard to its relation to the "roots." 

 In that species, according to Spengel, the dorsal septum only exists 

 in the posterior part of the collar; two "roots" are situated 

 anterior to it, and its anterior free edge always appears to corre- 

 spond to one of the "roots." In this species the septum ma}^ arise 

 in the anterior region of the collar and in front of the most 

 anterior root as a fold projecting from the dorsal surface of the 

 collar cord and with a free anterior edge, and which reaches the 

 outer wall where the first "root" fuses with the collar epidermis. 

 The septum then passes between the remaining "roots" to the 

 posterior end of the collar. Over part of its course it may be 

 interrupted: the ventral connection with the dorsal surface of the 

 cord is lost, the septum at the point of interruption appearing as 

 a free fold projecting from the inner surface of the outer collar 

 wall. Further, in other individuals the front edge of the septum 

 may coincide with either the first or the second "root." 



As to the ventral septum (fig. 19, vcs.) when present, it exists 

 only in the most posterior part of the collar and there only for a 

 very short distance. It may be present when the dorsal is absent. 

 In fig. 18 a section passing just anterior to the ventral septum is 

 represented. The vessel fold {sh.) arising from the subeiDidermic 

 collar capillaries exists only for a short distance in the posterior 

 region of the collar, and is not always so distinct as in the series 

 from which this section is taken: posteriorly it unites with one of 

 the longitudinal vessel folds to give rise to the ventral septum 

 (fig. 19, vcs.). The collar canals and the collar-trunk septum are 

 related in this species exactly as in Pt. minuta. 



