PROGRESS IN BIOLOGICAL INQUIRIES, 1926 623 
A plentiful supply of eggs of the pigfish was secured last May with a tow 
net in the channel between Pivers Island and the mainland; and as this is 
within 100 yards of the laboratory, the eggs could be examined with the loss 
of but little time. j 
Towings made shortly after dusk yielded the best results in furnishing eggs 
in the early stages, it being evident that spawning takes place principally at 
this time of the day. The eggs are comparatively large, being nearly 1 milli- 
meter in diameter; they are semitransparent and contain one large oil globule. 
Cleavage of the germinal disk takes place rapidly, so that the 2-cell stage 
is reached within half an hour, the 4-cell stage at 45 minutes, and the 8-cell 
stage at 144 hours after fertilization. After 24 hours several features of the 
embryo pigfish are discernible, including the snout and eyes, with the dorso- 
ventrally flattened body, consisting of about 380 somites, extending around 
about one-half of the inner circumference of the egg. At 36 hours the embryo 
has assumed a more cylindrical form and has grown so as to encircle almost 
completely the inner circumference of the egg. The heart and the auditory 
vesicles are quite evident. During this process the yolk, of course, has de- 
ereased in bulk, so that at this stage it is perhaps only two-thirds its original 
size. 
The period of incubation in this species is about 48 hours. Upon emerging, 
however, the young is considerably handicapped by the large elliptical yolk 
sae, which is equal to one-half the total length of the larva. The young pig- 
fish, nevertheless, is quite active at this stage. 
At about 2% days after hatching, or at 4144 days after the egg was fertilized, 
the young pigfish had attained a length of 3 millimeters, the pectoral fins 
had appeared, and several characteristic chromatophores were evident. The 
yolk was virtually absorbed, with the exception of the oil globule, which was 
less than one-half its original size. The median finfold extended from the 
nape completely around the body, terminating at the throat. 
The young, up to this stage of 3 millimeters in length, had developed in a glass 
dish in the laboratory, but due to some unknown cause several lots of fry 
expired upon attaining this size and none was carried to the next stage in the 
laboratory. The next stage available for study had attained a total length 
of 7 millimeters. These presented a considerably altered appearance, when 
compared with the preceding stage; the continuous median finfold had dis- 
appeared and was replaced by distinct dorsal, caudal, and anal fins, all with 
fairly distinct rays. This stage, however, scarcely resembled the adult in a 
single feature, the profile being concave, with the pineal fontanelle quite evi- 
dent. Young of this class were found to frequent the more protected shoals 
around Pivers Island, where protection was provided by a close marginal 
growth of sedges. 
This stage, represented by the concave profile, is very transitory, as fry 
only a few millimeters longer have a notably convex profile and the pineal 
vestige has entirely disappeared. ‘The fins in these young pigfish of 11 milli- 
meters retained virtually the same form as those of the preceding stage, with 
the exception that the spinous portion of the dorsal had commenced to make 
its appearance in the form of several tubercles somewhat anterior to the soft 
dorsal, which was already formed through a modification of the origina 
median finfold. 
In fish having a length of 15 millimeters the spinous dorsal is well developed, 
but there is a noticeable interval between it and the soft dorsal, although in 
mature fish these fins are jnined. Scales have not yet been developed; <he 
myomeres are quite distinct. 
Young 1 inch in length may be recognized easily as pigfish, differing from the 
adult form principally in having enlarged eyes and a broad lateral stripe. 
The ingested material in 100 young, ranging from 10 to 93 millimeters in 
standard length, was examined for the purpose of gaining some idea as to the 
progressive change in diet as the fish increase in size. Young of from 10 to 11 
millimeters in standard length were the smallest in which the stomach contents 
could be identified definitely. Several of such fish had taken a few very small 
copepods. These minute crustaceans continue to be taken in considerably in- 
creasing amounts until the fish attains a length of approximately 30 millimeters, 
when chztopods are taken, after which the copepod becomes less evident and 
seldom is found in specimens over 60 millimeters in length. Other small 
crustaceans, including Gammarus, ostracods, and Mysis, supplement the 
copepods in the diet during these early stages; and even the larger sizes, up ta 
