DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 813 



sea at both surface and bottom from March to May,* and have a diameter of '0551 inches 

 or 1*375 mm. The embryo emerges from the 8th to the 10th day in April, and in 

 May somewhat earlier. 



Thus those which on the 16th April presented the multicelled lenticular stage with 

 the nucleated periblast surrounding the disc, next day, at 9.30 a.m., showed a still 

 larger number of nuclei in this zone, which, however, at 1 p.m. had all but disappeared, 

 while the blastodermic ring had increased in size. On the 18th April the blastodermic 

 ring extended over a third of the surface of the ovum, and two hours later it had gained 

 the equator. At 3 p.m. the keel of the embryo had deepened, and faint indications of the 

 optic enlargements were visible, while at 4 p.m. they were completed.! At 10 a.m. on 

 the 19th the embryo was fully outlined, with five or six protovertebrse. The blastopore 

 had closed, and there were traces of Kupffer's vesicle. At 12 noon the protovertebrse 

 had doubled, and Kupffer's vesicle was more distinct. The invagination of the lens had 

 commenced, and the alar membrane of the embryo was distinct. 



20th April. — The eyes, otocysts, and mesenteron (which turns to the right) had all 

 made progress, and the heart showed a double-celled appearance at 3 p.m. The otoliths, 

 at first very small, occurred at 4 p.m., and the pectorals were outlined. 21st April. — 

 The body of the embryo jerks from side to side, and the heart pulsates languidly and 

 irregularly (about 3 p.m.), the contractions, however, sometimes ceasing for fifteen or 

 twenty seconds. The trunk has lengthened and the caudal extremity is flexed. The 

 pectorals are more distinct, and the delicate processes anterior to the fins (observed in 

 most forms) still persist. The mesenteric lumen extends as far as the heart, and 

 enlarges in the mid-region. The notochord is now completely crossed by intermingling 

 arcs. 



22nd April. — The posterior region of the trunk and tail are now flexed, and the yolk 

 appears to have decreased. The pectorals are well defined and pointed posteriorly, 

 while the anterior margin is rounded. The liver forms a rounded process, the heart 

 shows a venous end, and the pulsations are more regular (twenty-five per minute). 

 Round chromatophores (black) have appeared on the head and dorso-lateral regions of 

 the trunk, but they have no regular linear disposition. 



23rd April. — The eyes show pigment, and that over the body has increased. Three 

 branchial clefts and the nasal pits are visible. The violent motions of the embryos 

 indicate their advancement, and a few issued from the eggs. The empty capsules retain 

 their spherical shape, though a rent passes two-thirds across their diameter. 



24th April. — Five-sixths of the embryos are still in the eggs. They present a similar 

 appearance to the previous day, though the increasing complexity of the branchial region 

 is evident, and four clefts are visible. Some of the chromatophores on the head are 

 stellate. 



* Mobius and Heincke state that the cod in Kiel Bay spawns from January to the end of March, but in other 

 parts of the Baltic, e.g. Gothland, in April ; op., cit. p. 233 (1883). 

 t The temperature of the laboratory was 59° F. 



