Oll the larval developnient of Araia calva. 



653 



that the pcrfectioii in the fin Supports takes place in the following 

 Order in time, 1) dorsal, 2) anal, 3) caudal, 4) pectoral, 5) ventral. 

 In the pectoral flu the increase in the number of the radials takes 

 place in the region of the ventral (i. e. posterior) tin margin, near 

 the enlarged base of the flu. The ventrals, v., are now elongated, 

 lappet-like. In the head region the mucous canals exhibit but few 

 advances; the tube-like outgrowth of the anterior naris, a.w., is note- 

 worthy; the enlarged size of the opercular flaps causes their broad 

 overlap ventrally; in the gular region, however, they are overspread 

 by the growth of the jugular plate, jug. This maintains at its distal 



Radialia in larva of days 



15 



22 



35 



Adult 



Dorsal 



Anal 



Caudal 



Pectoral 



Ventral 



58 

 13 

 24 

 22 

 9 



end dermal connection with the ridges of the ceratohyals. To this 

 ridge are now appended the branchiostegal rays, a dozen in number 

 as in the adult. These begin ventrally near the jugular region small, 

 tapering, slender, and increase in size as their series passes lateral 

 toward the opercula, with which, indeed, they appear in close serial 

 homology. The exhaustion of the yolk material takes place during 

 the final part of the larva's second week, and results outwardly in 

 the closer modelling of the wall of the abdomen and that of the trunk. 



Larva of about the twenty -second day (PL 11, Fig. 22; 

 dorsal aspect PI. 11, Fig. 23; ventral PL 11, Fig. 24). 

 The following advances characterize this stage : the marked out- 

 growth of the caudal fin, c. ; the outlining of the definitive anal, and 

 the reduction of the larval caudal-anal and pre-anal fin-fold, c-a. and 

 ant. an. ; the closer welding of the line of muscles of the basal fin 

 Supports with the muscles of the trunk; the distal broadening of the 

 ventral fins; the first appearance of scales in the anterior region of 

 the lateral line; the outlining of the pre-, sub- and iuteropercula. 

 A broad transparent linea alba, Z. a., permits a glimpse of the 

 ventral viscera, notably the ventricle and the conus and bulbus 

 arteriosus. 



