History of a transient nervous apparatus in certain lohthyopsida. 415 



Appendix b. 



The comparison with Rabl's finds in Prisfiurus in the following 

 summary may be useful: 



state of gill-slits, 



2 pouches. 



3 pouches. 



4 pouches, of which the first branchial is opening. 



5 pouches, of which the spiracle and first and second bran- 



chials are open. 



85 — 90 — 4 pouches (fifth forming), of which first and second 



branchials usually open, 



100 — 101 66 — 68 5 pouches formed, sixth in formation, 3 open and a 



fourth on point of opening. 



104 74 all 6 formed, 4 open and a fifth on point of opening 



111—124 — 5 open. 



135 — 6 open. 



It is difficult to bring the two tables into exact correspondence, 

 for there is some variation on Baja in the period of the actual 

 rupture of the various pouches. Thus in No. 564 the spiracle has 

 lagged behind and is still closed, although the third branchial is open 

 on one side. Rabl correct ly states that the spiracle usually only 

 opens after the first and second branchials. 



