554 D. L. GAMBLE 



3. The rib-bearer and the parapophysis approach end to end, 

 while in the trunk region they meet at an angle of 90°. 



4. The rib attaches to the rib-bearer and has no connnection 

 with the parapophysis. 



On one side of the second vertebra of the 24-mm. larva ventral 

 and lateral cartilages are both present and continuous proximally 

 (fig. 18, p.a., h.a.). On the other side lateral cartilage only is 

 present, the haemapophysis Qi.a.) having disappeared at the 

 onset of bone formation. On the side where both elemejnts are 

 present, the basal stump appears as a forked structure in which 

 growth is taking place in two directions dorsolaterally and 

 ventrally. The lateral outgrowth does not quite meet the carti- 

 lage of the rib-bearer, the two being separated by mesenchyme. 

 The rib proton is continuous with the rib-bearer. On the other 

 side the connection between the parapophysis and rib-bearer is 

 almost made, the two being separated by a very narrow zone of 

 procartilage. 



In the third vertebra the parapophysis is still unconnected 

 with the rib-bearer, and the rib proton extends laterally from it 

 (fig. 19, p.a.). The cartilage of the rib has developed mesally 

 and is separated from the rib-bearer by a limited zone of procar- 

 tilage cells. 



The fourth vertebra of this larva is very important in eluci- 

 dating the morphology of the rib-bearer, basal stump, and rib 

 (fig. 20). On the left side the basal stump projects laterally from 

 the notochord and is continuous distally with the rib-bearer, as 

 in the stages previously described in the trunk region. The rib 

 is borne, also as in the trunk region, at the point of union of 

 these two elements (r). On the right side the parapophysis was 

 tardy in development as compared with the left, and is seen pro- 

 jecting laterally a very short distance and making no connection 

 with the rib-bearer whatever. The rib is borne by the rib-bearer 

 and has no connection with the basal stump. 



This condition cannot be explained on the basis of Goeppert's 

 interpretation of the morphology of these structures (fig. 1). 

 Here the development of the parapophysis has lagged behind 

 that of the rib-bearer and the rib has become attached to the 



