GIBSON— CEPHALOCHOED A : " AMPHIOXIDES." 



251 



although the general homologies which have been drawn between the vascxilar systems 

 of the two groups can hardly be held to be prejudiced by the dispositions — often obviously 

 secondary — found in Amphloxides. 



It would be unproiitable to enter here into a discussion of the vexed questions of the 

 segmentation of the head, with which Goldschmidt deals in the last section of his 

 monograph. But there is one aspect of the problem, brought into prominence by the 

 study of Amphioxides, and important in connection with the discoveries and speculations 

 of Van Wijhe, with which he has not dealt, viz , the relation of the ventral coelomic 

 cavities in the anterior region of Amphloxides (no doubt closely paralleled in the 

 Branohiostoma larva) to those in the adult Braiichiostoma. 



A striking change, the most essential features of which may he understood from the 

 accompanying diagrams, is seen to affect the splanchnoccele as we pass from larva to 

 adult. In Amphiuxldes this forms a single continuous cavity, surrounding the gut on 



Lymph - c&nats 

 Replacins Ventral 

 nostrdi- Cavity 



Fig. 4. — Diagrammatie horizontal sections through the heads of Ampldoxides pelagicus (left) and adult Branchiostcraa 

 lanceolatum (right). The gill-slits are shown as clear areas ; coelomic cavities lightly shaded : darker 

 shading indicates solid tissues. L.C.E., R.C.E. : left and right " cava epipterygia." 



three sides as far as its extreme anterior end, interrupted only by the gill-slits and mouth : 

 anteriorly it communicates on the right-hand side with the cavity of the 1st myotome. 

 In the adult Branchiostoma, on the other hand, the epibranchial coelom does not extend 

 farther forward than the 1st pair of gill-slits, at the level of which it is separated by an 



