A gynandromorph of the brine shrimp, Artemia salina.

S EXUAL mosaics have been reported in three genera of Crustacea. A bilateral mosaic of Carcinus was found to have a testis on one side and a mixed gonad on the other (VEILLET 1945). Gynandromorphs with a testis and ovary have been reported in Homarus (see review by CHACE and MOORE 1959) and in the cladoceran, Simocephalus (BANTA, WOOD, BROWN and INGLE 1939). No intersex or mosaic of Artemia has been reported previously. The method of sex determination in Artemia is of interest because one bisexual race and many parthenogenetic races have been reported to be polyploid (BARIGOZZI 1957; BARIGOZZI and TOSI 1959). The cytological studies of Artemia (reviewed by BARIGOZZI 1957) have not demonstrated the presence of heterochromosomes nor a difference in chromosome number in the two sexes. Although no studies have been made of sexual differentiation in Artemia, extensive studies have been made of another crustacean, Orchestia gummarellus. CHARNIAUX-COTTON ( 1960) has demonstrated that differentiation in this amphipod is mediated by a male hormone produced by an androgenic gland. Homologous male and female tissues respond in the same manner to the hormone. Therefore, the hormone suppresses the normal differentiation of genetically female tissue. In the following morphological descriptions, we have used the terminology of LOCHHEAD (1941, 1950) with few exceptions. We have adopted the term uterus used by GOLDSCHMIDT (1952) to designate the organ in which the eggs undergo segmentation. We use the terminology of CASSELL (1937) for the male reproductive system. External sexual dimorphism in Artemia is seen in the larger size and modified shape of the male antennae. The male has a penis on each side of the body, whereas the female has one median ovisac. The male has two separate reproductive systems, one on each side of the body. Each consists of testis, seminal vesicle, and vas deferens. When the penis is retracted, the seminal vesicle is folded in a U-shaped loop. During copulation, the penis is everted, the seminal vesicle is straightened, and the inner surface of the vas becomes the outer surface of the penis. The female reproductive system consists of two ovaries, two pouch-like oviducts, and a median uterus which lies within the ovisac. Attached to the uterus are four clusters of shell glands.