444 EMBEYOLOGY OF THE LOWER VERTEBRATES CH. 



A//;/ ids) in those various groups of Lizards which have developed 

 an elongated snake-like form. So also in Snakes. 



In cases where the limbs are completely gone in the adult it may 

 be possible to observe them during early stages of development. 

 The young Symbranchus (Fig. 203) has for a time huge pectoral fins 

 which it uses as organs of respiration (Taylor, 1914). In Gymno- 

 phiona and Blind worms (Anguis) l minute limb rudiments have also 

 been observed in the embryo. In other cases no trace of the missing 

 limbs has been found during early development. In view of this 

 general tendency of the limbs to disappear in Vertebrates which 

 have assumed an eel-like or snake-like form of body it is well, as 



01 2345 



0:0. 



2 3 



I 'i<;. 203. Symbranchtta marmoratits. Larvae showing pectoral fins. 

 (After Taylor, 1914.) 



.!, opi-rciilar opi-nin- ; .--./. r. subinti-sliiKil vein ; y, yolk. 



already indicated, not to assume a dogmatic attitude in regard to 

 sucli Vertebrates as Lampreys or Hag-lishes. The possibility is not 

 excluded that even these Cyclostomes are descended from ancestors 

 in which limbs were present. 



The interesting question now run -r^es How did the limbs of the 

 Vertebrate ori-jinai.- in evolution '. Few morphological speculations 

 have excited more interest and more controversy than this. Two 

 main hypoi h606fl ha\ < been propounded ami each has round supporters 

 amongst the most eminent, niorplmln : jists. Although in the opinion 

 of tin present mil r it is no Ion--'-!- necessary to fall hack upon 

 eit.h.-r of ill,. inijiler pn-nhdity having presented itself, a, 



1 The i'kmi:iit;iry .stmli-nt in.iy !> uaimd not to mi.stukr tin- i inliiiK'iil- ut' tin- 

 |..iir.-.| j.-n.-s in Sn.-ik.- i-!iil.ry.s for llmbf ! 



