786 BEPOET OF COMMISSIONER OF FISH AND FISHEEIES. [8] 



composed of very fine interlacing fibers, as in the adult, I am unable to 

 state. 



The palps or lips of the young spat at this stage are not at all like 

 the palps of the adult. They are much shorter, as indicated -dtp, but 

 the upper or anterior lip passes like a hood in front of the mouth o, and 

 the lower, hinder, and inner one bends backwards on either side behind 

 the mouth. In the adult, the inner suiface of the outer pair of palps 

 or upper lips are furrowed with numerous shallow grooves ; in the lower 

 lip the outer and upper surfaces are so furrowed. lu the young, a dif- 

 ferent state of affairs exists. Here furrows can scarcely be said to be 

 l^resent ; but the lips are apparently divided into more or less distinct 

 conjoined parallel lobes; their number, unlike in the adult, is also very 

 few, or about 4 to 5. I have counted over one hundred folds and fur- 

 rows on one side of the lower lip or palp of the adult: we would nat- 

 urally expect to find them fewer in number on the same parts in the 

 young animal. 



At the hind or ventral borders of the palps their edges seem more or 

 less nearly continuous with the gills, and, as there are four of the latter 

 as well as four posterior ends to the lips, it would appear probable that 

 both palps and gills originated from very nearly the same primitive 

 structure. That is, suppose the four folds or rows of branchial processes 

 of which the gills are formed were at first developed from a tract of 

 epiblastic tissue, or the skin-layer proper, from which the palps also 

 are differentiated, and it is possible to conceive of them as having been 

 developed from nearly the same type of rudiments, that is, longitudinal 

 folds of epiblast which were at first continuous. 



The mouth of the spat in Fig. 2 opens downwards and not so directly 

 forwards or dorsally as in the adult. This fact, taken in connection 

 with the singular change of place undergone by the mouth in its pas- 

 sage from the fry stage to that of the spat, is significant and will be 

 discussed farther on. 



The ciliated band c in Fig. 2 gives an ideal representation of the way 

 in which the cilia on the inner surface of the mantle are arranged and 

 how they may be brought to act in conveying the food to the mouth o. 

 The gills also are of course clothed with cilia, as in the adult. 



The course of the intestine i is very much the same as in the adult; 

 the vent a lies just over the adductor muscle m, and the stomach s is 

 enveloped by the brown liver /, which appears to constitute the principal 

 portion of the body-mass, exclusive of the intestine and stomach, at 

 this stage. The heart is divided into a pair of auricles, x, below and a 

 medially divided ventricle, z, above, and like the heart of the adult, lies 

 in a crescent- shaped heart-caAdtj'. Where the intestine returns and 

 bends sharply backwards on itself above the mouth, there is a rounded 

 projection of the body-mass forwards, which is not seen in the adult. 



The most striking changes in the relations of the intestine after the 

 larval condition is past and that of the young oyster has been assumed 



