EMBRYOLOGY AND LARVAL DEVELOPMENT OF TELEOSTEAN FISHES. lOQ 



the body remains yellowish. Black chromatophores occur sparsely scattered over the 

 dorsal and lateral aspects of the body and in a series along the ventrolateral aspect of 

 the body near the base of the ventral-fin fold. 



In young fish 8 to lo mm. in length (fig. 47) the dorsal, anal, and caudal fins are 

 becoming well differentiated, and the free rays of the pectoral fins characteristic of the 

 species are already present. The general color of the body and the distribution of black 

 chromatophores remain essentially as in the preceding stage. 



In young fish 25 to 30 mm. in length (fig. 48) the general color of the body has become 

 darker, and the trunk is marked by heavily pigmented areas that give it a transversely 

 banded appearance. The fins are well differentiated. The head is long and somewhat 

 pointed and shows the bony structure characteristic of the adult. The young fish are 

 gradually assuming the appearance of the adults and already show many of the diag- 

 nostic characters of the species. 



MERLUCCIUS BILINEARIS (Mitchill). WHITING. 



Spawning. — Eggs of this species were present in small numbers in the plankton late 

 in July and throughout August. Males ripe for stripping and females nearly ripe were 

 taken in the traps in Menemsha Bight late in July. A few females apparently ripe for 

 stripping were taken in the same traps on August 6. The eggs were successfully fertilized, 

 but all died during early cleavage. The majority of the fish taken in these traps on 

 August 16 were smaller than those taken earlier. Among them were found a number 

 of spent females, but none ripe for stripping. Apparently the spawning period for this 

 species is a protracted one and not all the eggs mature at one time. 



Eggs. — The eggs are highly transparent, spherical in form, and 0.88 to 0.95 mm. in 

 diameter. The yolk sphere contains a relatively opaque, yellowish or brownish oil 

 globule 0.19 to 0.23 mm. in diameter. The protoplasmic layer is finely granular. The 

 egg membrane is thin and homy. 



Embryology. — The embryological development of this species is entirely typical and 

 does not differ essentially from the course of development as outlined for Tautoga onitis. 

 Early and advanced stages of cleavage are illustrated in figures 50 and 51. 



Pigmentation begins soon after the closure of the blastopore. At this time the 

 embryo extends approximately halfway around (he circumference of the yolk sphere. 

 Black chromatophores become sparsely scattered ever the embryo and the oil globule. 

 The extra-embryonic blastoderm remains free from pigment. The distribution of 

 chromatophores several hours after the beginning of pigmentation is illustrated in fig- 

 ure 52. 



As the time of hatching approaches (fig. 53), yellow pigment also becomes apparent 

 on the embryo. Yellow pigment areas occur just back of the eye, back of the otocyst, 

 in a series along the lateral surface of the anterior region of the trunk, and in two vertical 

 bands on the posterior half of the body. The distribution of black pigment on the 

 anterior half of the body remains essentially as in the earlier stages. Farther posteriorly 

 all the black chromatophores have become aggregated in two vertical bands. 



Larval development. — Incubation occupied not over 48 hours. The newly hatched 

 larvae (fig. 54) are approximately 2.8 mm. in length and relatively slender. The head 

 is slightly deflected at the anterior end of the yolk sac. The vent is located immediately 

 69571°— IS 8 



