122 BULLETIN OF THE 
sperm. Many eggs can be washed out of the undissected sea-urchin 
with a pipette introduced through the aboral region. The floating eggs 
and the milky sperm are mixed by simply pouring the water from one 
jar to the other. A better method of artificial fecundation is to collect 
a watch glass crystal full of eggs, leaving enough water for them to 
float, and then to drop a few drops of water charged with sperm among 
them. The contents are then gently stirred, and after a short time 
evidences of the success of the process may be looked for. I have 
found that chopping up the two glands together, although in some cases 
to be recommended, in most instances, and especially in the case of 
Echinarachnius, the egg of which is delicate, leaves so much decaying 
matter that the ova are killed. It is well not to put too much water 
with the ova, as repeated dilution renders the collecting of the ova for 
study difficult. I took no precautions about the temperature of the 
water, and did not find it necessary to change the water until after 
segmentation was finished.* Artificial fecundation was accomplished 
from the middle of July to the end of August. i 
Each ovum, PI. Il. fig. 1, is visible to the naked eye. It is sur- 
rounded by a viscous? layer in which are beautiful, spherical or some- 
times angular, red pigment spots, pig, which are supposed to correspond 
to the “clouded areas,” described by A. Agassiz f in the star-fish egg. 
The viscous layer of the egg of H. esculentus is described by Derbes. 
A. Agassiz describes a “thick homogeneous structureless shell” in 
Strongylocentrotus. The pigment spots are conspicuous on the outer 
surface of the viscid capsule of the egg of Echinarachnius. After fer- 
tilization the ova sometimes sink and sometimes remain floating. Their 
specific gravity is about that of the water. 
The diameter of the yolk, 2, is.13 mm. The diameter of the viscid 
covering is from .22 to.25mm. The yolk is yellow ; the envelop trans- 
parent. The yolk was not observed in the free egg to fill its capsule in 
any stage of segmentation. 
A nucleus and nucleolus were observed in ovarian eggs. These 
structures were difficult to see in free eggs. 
The spermatozoa immediately after the mingling of the two sexual 
* Selenka and others have already pointed out refined ways of fertilizing sea- 
urchin eggs. See Selenka, “ Keimblatter und Organenlage der Echinodermen.” 
Zeit. f. Wiss. Zool., XX XIII. p. 40. 
+ Similar pigment spots are found according to Nachtrieb in the egg of Mellita. 
These spots on the ovum of Echinarachnius were first described in my paper on the 
development of Arbacia. Mem. Peabody Acad., I. 6. 
