282 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVIT. fig. 4) has also greatly increased in length from that of Plate 

 XVII. fig. 3, tho original pectoral ray at the same time having be- 

 come so bent that the extremity forms an obtuse angle with the base. 

 The separation of the anterior from the posterior dorsal takes place 

 at a very early stage, already within the egg (Plate XVI. fig. 3), the 

 first ray of the anterior dorsal pushes its way through the embryonic 

 dorsal fold in a slight depression formed above the head, and thus 

 forms the separation of the anterior part of the dorsal embryonic fold 

 from the posterior. In a view from above of the young Lophius 

 within the egg, the derivation of the pectorals and of the ventrals from 

 the embryonic fin fold which covers the yolk bag is well seen. The 

 paired fins are formed in the same manner on the yolk fold. They 

 belong to the original embryonic fin fold, which splits, so as to cover 

 the yolk bag. 



Plate XVII. fig. 6, represents the embryo Lophius in a somewhat 

 older stage than when the dorsals and ventrals are in stage figured 

 on Plate XVI. figs. 4, 5. The dorsal and ventral embryonic folds are 

 somewhat more opaque, both from the greater number of pigment 

 spots, which, however, are of lighter tint than in younger stages, and 

 from the additional number of embryonic fin rays. These are now 

 very closely placed together on the dorsal side ; they are somewhat 

 less numerous and more distant on the ventral side. This stage is 

 remarkable also for the great size of the lobed fleshy pectorals, with 

 rows of light gray dendritic pigment cells along the line of the em- 

 bryonic rays. There is a rudiment of a third dorsal ray, and the 

 second ray of the ventral is more than half as long as the original 

 ray. Teeth are well developed on the lower jaw. In the next stage 

 figured (Plate XVIII. fig. 1) the principal dififereuces consist in tlie 

 increased length of the anterior dorsal rays (there are three rays now, 

 and the rudiment of a fourth), the increase in length of the two ventral 

 rays and the appearance of a rudiment of a third ray. Muscular 

 bands are now more distinct along the body than in the younger 

 stages ; the three principal pigment spots have become broken up into 

 smaller dendritic pigment cells, and we have the first trace of the 

 formation of a caudal fin in the widening of the body immediately 

 below the anterior part of the caudal pigment spots. The fleshy 

 pectoral has become still larger than in the last stage figured ; the 

 dendritic stellate chromatophores of the head and of the ventral region 

 of the pectoral side of the body are more numerous ; the head has 

 greatly increased in size, it is colored light yellow ; the muscular bands 



