Asyiivnietron hassaniiin, Gimther. 87 



from the body wall, except on the ventral surface (Figs. 3 and 

 4). The left post-atrioporal caecum stops a short distance 

 behind the atriopore (Fig. 5) ; the right is longer and extends 

 almost to tlie anus (Fig. 6). 



In Fiu'. ."^ the relative lengths of the caeca and coelom are 

 represented. 



Taking the distance between the termination of the right 

 atrioporal caecum and the anus as one, the following are the 

 relative proportions: — 



Between the atriopore and the posterior termination of the 

 left atrial caecum — 8. 



Between the posterior termination of the left caecum and 

 the posterior end of the right — 20.5. 



Between the end of the right caecum and the anus — 1. 



Extension of coelom behind the atriopore, i.e., to the anus — 

 29.5. 



4. — Coelom. 



The coelom extends from the anterior end of the body to 

 the anus. In the region of the pharynx it is much I'educed by 

 the atrial cavity being represented by paired cavities on its 

 dorsal surface, with prolongations down the primary gill-bars 

 communicating with the endostylar coelom on the ventral 

 surface. Beyond the pharynx it is a small cavity surrounding 

 the intestine, the atrium occupying the greater part of the 

 sjDace within the body wall. Just beyond the atriopore the 

 coelom is still confined to a small space owing to the prolonga- 

 tion of the atrial cavity (Fig. 2), and becomes more spacious 

 as the caeca die out (Figs. 3, 4, 5, 6), and ends in the region 

 of the anus (Fig 7). 



5. — Classification. 



There is some uncertainty as to the position of Asi/mmetron 

 hasxanum. Miss J. W. Kirkaldy, in a paper in the Q.J. M.S., vol. 

 xxxvii., divides the family Brancliiostomidae into two genera— - 

 Branchiostoma and Asymmetron. The former she sub-divides 

 into tAvo sub-genera — Amphioxus and Heteropleuron — and 

 classifies the species in question as Heteropleurnn hassanum. 

 But the chief features m the species — viz., the unilateral 

 nie:apleural folds, and the single series of gonads, were found 



