16 W. B LAX LAND BENHAM. 



vessel communicating with the branchial artery. 5 ' Lankester, 

 from its relation to the subendostylar coelom, regarded this 

 canal in the rod as "coelom;" whereas Spengel and Boveri 

 look upon it as a blood-vessel, and deny its ccelomic character. 

 Lankester gives half a dozen figures (loc. cit., pi. xxxvi B, figs. 

 5 9) of as many consecutive sections representing the canal 

 communicating with the subendostylar coelom. Spengel denies 

 this altogether, and states that the rod becomes solid before 

 it reaches the endostyle, and there becomes continuous with 

 the subendostylar skeleton. He further denies any communi- 

 cation of this rod cavity with the dorso-pharyngeal coelom. 



Now the tracing of these cavities is an extremely difficult 

 matter, owing to the difficulty of making sections in the right 

 plane, and I searched through section after section before I 

 could satisfy myself as to the mode of termination of these 

 rods. Time after time it seemed to me that Speugel was right, 

 so far as the non-communication of the rod cavity was con- 

 cerned ; but in certain lucky sections I found that the plane 

 was convenient for this purpose, and I represent five consecu- 

 tive sections which show, as I believe, the continuation of the 

 subendostylar coelom into the cavity of the rod (PI. 7, figs. 

 22 26). The series shows most certainly no continuity be- 

 tween the rod and the subendostylar skeleton on which Spengel 

 insists. 



I was not successful in tracing the rod cavity into the dorso- 

 pharyngeal coelom ; but I attribute this to the difficulty of ob- 

 servation, and am by no means inclined to conclude that such 

 a connection does not exist. 



The " skeletal vessel " ceases some little way before the rod 

 does, being connected with the vessels in. the neighbouring 

 primary bars at the lowest synapticulum. 



If the hinder gill-slits be examined in a preparation of the 

 pharynx, flattened out on a slide, and the mode of development 

 of the " tongue " observed, it will be seen that the rod in the 

 tongue is double at its upper end; the two pieces diverge 

 and constitute the arcade connecting the series of rods. The 

 tongue bar, as is known, is a dowugrowth from the upper 



