1 62 ELEMENTARY BIOLOGY. [CHAP. 



Examine from the side. 



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

 tional sense organs. 



yS. The external branchicB ; long and pectinated ; 

 three in number on either side, a small third- 

 pair having appeared. 



y. The tail ; elongated and marked out into 

 number of well-defined segments {myofneres). 



8. The median fin ; 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 (cloac 

 orifice). 



Examine from beneath, 

 €. The mouth; transversely enlarged and sur 

 rounded by fleshy lips, within which can be seen 

 the jaws, beset by small horny teeth. 



/. The lari'a, at a later period. Look for larvae in"' 

 which the external branchiae of the right side are 

 no longer visible. Examine from beneath. H 



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

 foregoing stages, as to relative proportions. ■! 



^. The external branchice ; visible only on the left 

 side, projecting out from beneath a fold of the 

 cephalic integument {operculum). A similar fold ^ 

 is seen on the opposite side. H 



y. The mouth; transversely oval and very large; 

 the lips^ now papillate ; horny teeth, more 

 marked. 



8. The suckers ; disappearing, and reduced to the 

 condition of a couple of small tubercles. 



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