﻿162 ELEMENTARY BIOLOGY. [CHAP. 



Examine from the side. 



a. The Jiead ; well marked and possessed of func- 

 tional sense organs. 



/j. The external branchice ; long and pectinated ; 

 three in number on either side, a small third- 

 pair having appeared. 



y. The tail ; elongated and marked out into a 

 number of well-defined segments (myomeres). 



The median Jin ; a thin fold of integument en- 

 circling the tail and continued forwards dor- 

 sally to the middle of the back ventrally, for 

 a short distance in front of the anus (cloacal 

 orifice). 



Examine from beneath. 



c. The mouth ; transversely enlarged and sur- 

 rounded by fleshy lips, within which can be seen 

 the jaws, beset by small horny teeth. 



/. T/ic larva, at a later period. Look for larvae in 

 which the external branchiae of the right side are 

 no longer visible. Examine from beneath. 



a. Head, trunk and tail. Cf. generally with the 

 foregoing stages, as to relative proportions. 



P. The external branchicz ; visible only on the left 

 side, projecting out from beneath a fold of the 

 cephalic integument (ope rail urn]. A similar fold 

 is seen on the opposite side. 



y. The month ; transversely oval and very large ; 

 the lips, now papillate ; horny tectJi, more 

 marked. 



<$. The suckers ; disappearing, and reduced to the 

 condition of a couple of small tubercles. 



