MUSEUM OF COMPARATIVE ZOOLOGY. yall 
adult pluteus is very different from that of either Arbacia or Strongylo- 
centrotus, and most closely resembles the pluteus described by Miller 
as that of the genus Echinocyamus. 
Artificial Fertilization. 
The sexes of Echinarachnius are distinct, the male and female organs 
being found in different individuals. Although the colors of the adult 
of different specimens vary, and in some instances it was possible for 
me to tell the sex without dissection, this could not be done in all 
cases. The colors of the ripe glands, ovaries and spermaries, can easily 
be distinguished. The former are commonly dark-red or purple ; the 
latter orange or yellow. 
Derbes* was not able to distinguish the male from the female of 
E. esculentus by external characters. The sperm according to him has 
a milky white color, and the ova are orange or brown. 
The males and females of S. drébachiensis, according to A. Agassiz,t 
are distinguished by a “more vivid coloring of the spines of the latter, 
which are of a violet tinge, while those of the males are more yellowish- 
green.” The ova and sperm of Strongylocentrotus, he says, resemble 
in color that of #. esculentus as described by Derbes. 
My method of procedure in artificial fecundation is as follows: The 
apical portion of the aboral region is incised through the test by a ring- 
shaped cut, with a radius equal to that of the petaloid openings. This 
dissection is carried on with the sea-urchin under water. The incised 
part is turned over, and transferred to a glass dish with water, and the 
remainder of the animal is placed in pure sea-water. 
Upon the inner surface of the incised part fragments of the ovaries 
will be found, if the specimen is a female, and spermaries if a male. In 
the former case, if the eggs are mature, small transparent globules will 
be found to float away from the glands, especially if the organ is slightly 
washed with a pipette. If a white fluid exudes from the glands the 
specimen, if alive, is probably a male, and the white fluid is colored by 
No. 6. H. Garman and B. P. Colton, some Notes on the Development of Arbacia 
punctulata Lam. Studies Biol. Lab. Johns Hopkins Univ. II., pp. 247-255, and W. K. 
Brooks, Handbook of Invertebrate Zoology for Laboratories and Sea-Side Work, 
figs. 78-83. 
* Observations sur le Mécanisme et les Phénomeénes qui accompagnent la For- 
mation de l’Embryon chez l’Oursin comestible. Ann. Sci. Nat. [8] VIII. 1847. 
+ Revision of the Echini, p. 708. 
