220 PROF. HtrXLET Olf THE 



it has not increased in proportion to the body ; but the cerebral 

 hemispheres are relatively larger, and the eyes are fully formed 

 and have moved backwards, dividing the sei'ies of myotomes into 

 a supraocular and a subocular bundle of muscles. And, in the 

 adult Lamprey, changes in the same direction have gone still 

 further. 



It is clear, therefore, that the region occupied by the six most 

 anterior myotomes of the body of Amphioxus answers to the prse- 

 auditory region of the skull in the higher Vertebrata. The ques- 

 tion next arises. How many of the succeeding myotomes are in- 

 cluded in the region which corresponds with the postauditory 

 or parachordal region of the skull in the higher Vertebrates ? 



The Lamprey has seven branchial sacs, with as many external 

 clefts; and no Vertebrate ever possesses more. To each of these 

 sacs nerves pass which undoubtedly correspond with the branchial 

 branches of the glossopharyngeal and pneumogastric nerves ; and 

 strong grounds for thinking that the pneumogastric trunk con- 

 tains tlie representatives of, at fewest, six primary distinct nerves, 

 answering to the six posterior branchial sacs, have been given by 

 by Gegenbaur and myself. If this be so, then the seven pairs of 

 nerves behind the representative of the portio dura in Amphi- 

 oxus will answer to the glossopharyngeal and pneumogastric, and 

 the eighth, somatome will correspond with the occipital segment 

 of the Ichthyopsida. Thus the skull of a Lamprey or of an 

 Elasmobranch fish is represented by the anterior region of the 

 body of the AmpMoxus as far back as the fourteenth myotome. 

 As there are from sixty to seventy myotomes, this estimate makes 

 the head of AmpMoxus to occupy, morphologically, one fifth of 

 the whole body. 



"With respect to the renal organs, Miiller thought he had ob- 

 served some rounded bodies which might have a renal character 

 in the posterior part of the abdominal cavity of living specimens 

 of AmpMoxus ; but as he could not find them by dissection, and 

 as no other anatomist has been more successful, they need not 

 now be discussed. 



liathke described two canals situated in the ridges which are 

 developed at the junction of the ventral with the lateral faces of 

 tbe body. He states that these canals open, behind, at the abdo- 

 minal pore, and in front at the mouth. Miiller and, more recently, 

 Stieda confirm Eathke's account, which appeared to be strength- 

 ened by Kowalew sky's statement that he had seen the ova pass 



