232 PEECT SLADEN TRUST EXPEDITION. 



This passage gives the key, I think, to the appearances found in Amphioxides . The 

 arrangement of the septa in the latter — more crowded anteriorly, more spaced out 

 posteriorly than the gill-slits — corresponds closely with that of the myotomes ; they are 

 evidently intermetameric. It would seem a not unlikely supposition, that the coelomic 

 pouch formed at the posterior, internal end of each septum represents the first 

 beginning of an excretory tubule, formed here at an earlier stage than in the Aniphioxius 

 larva, and actually seen to open at the hinder end of its segment as delimited by the 

 septum. If this is the case, we liave it actually demonstrated here that the excretory 

 tubules are at their first origin, in A . valdivice, metameric ; it is, unfortunately, impossible 

 to determine whether the same holds good of the right-hand series of giU-slits, since no 

 rudiments of these are yet present in the stage described. 



In connection with the excretory tubules, I must make brief allusion to other organs 

 of a supposed similar structure. The preservation of my material has not allowed me 

 to see anything of the solenocytes in " Hatschek's nephridium," and I can add nothing 

 to Goldschmidt's account of this. With regard to the enigmatical organs described 

 under the name of " Schwammkorper," the same cause has debai'red me from personal 

 observations. But it is difficult to credit Goldschmidt's account of their structure, and 

 M. Legros informs me that the appearances in the Amphioxus larva lead him to believe 

 that the structures taken for solenocyte tubules were in reality branches of the ascending 

 rami viscerales of dorsal nerves; in this region of the body the latter take a peculiar 

 course in septa cutting across the dorsal portions of the splanchnoccele {vide Legros, 

 1902). 



The Gonads. 



I did not find a single sexually mature specimen of Amphiuxides, nor any sliowing 

 the gonads in any but an extremely early stage of their development. Goldschmidt 

 only found gonads in 3 of his 29 specimens — one of which he regarded as approaching 

 maturity. There can therefore be scarcely any doubt that Amphioxides does not normally 

 become sexually mature in the state in which we at present know it. In the single 

 specimen supjiosed by Goldschmidt to be nearly mature, tlie gonads present remarkable 

 relations, lying in spacious ventral prolongations of the myoccele separated from the 

 myoccele proper — to judge from his figure — by horizontal epithelial septa. In Amphioxus, 

 on the other hand, they early come to lie in rhoraboidal pouches — " Genital Sackchen " of 

 Boveri (1892, ii.) — formed as evaginations of the ventral wall of the myocceles, which 

 soon lose their connection with the latter and hang down into the atrial cavity. The 

 condition found in the one Amphioxides is clearly an abnormality, due to precocious 

 development of the gonads in the absence of an atrial cavity — an exceptional case of 

 " individual neoteny." 



My specimens show perfectly normal conditions, the gonads being in much the same 

 state as that shown in Boveri's fig. 7 (1892, ii.) and in Zarnik's fig. £(1904). The 

 gonad appears in some cases to contain a cavity communicating behind with that of its 

 parent myotome. Zarnik found a similar condition. In no case has the stalk of 

 connection with the parent myotome been lost, and the future " Genital Sackchen," or 



