1889.] Embryology. 925 
activity. The resting stage begins immediately after the spawning ; 
the active stage begins a few months before spawning and culminates 
at spawning. During the resting period the eggs contained in the 
ovary do not perceptibly increase in size, while during the active stage 
they double their volumes many times. 
In Micrometrus the active period begins when the eggs are ripe, and 
culminates at the time the young are set free. In other words, the 
eggs become ripe when in ordinary fishes they only begin their most 
active growth. Now the yolk of normal fish eggs is found chiefly dur- 
ing the time of rapid growth ; maturation of the egg of Micrometrus 
being hastened several months, and occurring at the beginning of 
active growth, it is matured with but little yolk. 
In the young eggs of Micrometrus there lies a small nucleus exterior 
to the germinal vesicle. This nucleus increases in size, and in the ripe 
^gg lies directly at the vegetative pole of the ^gg. A similar structure 
is seen in Abeona. 
At or near the time of the shrinking of the ^gg it is freed from the 
ovarian follicle in which it was developed. By the shrinking of the 
egg a large chamber is formed between it and the membrane surround- 
ing it. About this time fertilization probably takes place. 
The spermatozoa deserve more than a passing notice. They are com- 
posed of a rod-shaped head and a long vibratile tail. Large numbers 
of them are found in the ovary, and the conditions for their continual 
activity being favorable they live in the ovary several weeks, very 
probably until they are digested by the young fish. They seem to in- 
crease in activity with their stay in the ovary. Their rapid motion 
keeps the fluid secreted by the ovary in constant circulation. This 
circulation is undoubtedly taken advantage of by the young, it bring- 
ing a large amount of oxygenated mucus in contact with them. If 
the spermatozoa were not present other arrangements for the circula- 
tion of the mucus would have to be provided, or the embryos and 
early larvae would undoubtedly be asphyxiated. 
The spermatozoa seem to have a triple function. First, the normal 
one of fertilizing the egg ; second, to circulate the mucus and thereby 
to aerate the embryo ; third, to act as pabulum to the larvse as soon as 
the digestive tract is sufficiently developed. 
The segmentation as far as observed is normal. It is apparent, how- 
ever, that inherited tendencies only keep the egg from segmenting totally. 
The stages from the completion of segmentation to hatching are not 
yet understood. 
