MUSEUM OF COMPAKATIVE ZOOLOGY. 121 



adult plutens is very different from that of either Arbacia or Strongylo- 

 centrotus, and most closely resembles the pluteus described by Miiller 

 as that of the genus Echiuocyamus. 



Artificial Fertilization. 



The sexes of Echinarachnius are distinct, the male and female organs 

 being found iu different individuals. Although the colors of the adult 

 of different specimens vary, and in some instances it was jjossible 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 milliy white color, and the ova are orange or brown. 



The males and females of »S'. druhachiensis, according to A. Agassiz.f 

 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 E. 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 Arhncia 

 punctulata Lam. Studies Biol. Lab. Johns Hopkins Unit-. IL, pp. 247-255, and W. K. 

 Brooks, Handbook of Invertebrate ZoiJlogy for Laboratories and Sea-Side Work, 

 figs. 78-83. 



* Observations sur le Mecanisme et les Phcnomenes qui accompagnent la For- 

 mation de rEmbryon cliez I'Oursin comestible. Ann. Sci. Nat. [3] VIIL 1847. 



t Revision of the Echini, p. 708. 



