. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 204 ANNALS OF THE SOUTH AFRICAN MUSEUM 5. Y-ORGAN This term v^^as proposed by Gabe (1953, 1956) for a paired organ which he observed in fifty-eight species of Malacostraca and considered to be similar to the prothoracic or moulting gland of insects. He has shown that in Decapoda and other Malacostraca in which the adult excretory organs are antennal glands the Y-organ occurs in the second maxillary segment, but is found in the antennal segment in forms having maxillary excretory organs in the adult.
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 204 ANNALS OF THE SOUTH AFRICAN MUSEUM 5. Y-ORGAN This term v^^as proposed by Gabe (1953, 1956) for a paired organ which he observed in fifty-eight species of Malacostraca and considered to be similar to the prothoracic or moulting gland of insects. He has shown that in Decapoda and other Malacostraca in which the adult excretory organs are antennal glands the Y-organ occurs in the second maxillary segment, but is found in the antennal segment in forms having maxillary excretory organs in the adult. Specific variations in its size, shape, and microscopic details have been reported, but it is generally located near the ventral body wall and has been interpreted by Gabe as a thickening of the hypodermis. Since Gabe's discovery, the Y-organ has been described in certain species by other investigators. According to Chaudonneret (1956), in Orconectes limosus {Cambarus ajjinis) it is an elongated mass situated between the mandible and the first maxilla and measures i -6 mm long, 0-6 mm wide, and 0-7 mm high: Passano (i960) has mentioned that the Y-organ oi Carcinus maenas is an ovoid structure which measures about 0-5 mm across and is located near the anterior end of the branchial chamber ventral to the mandibular posterior (external) adductor muscle. In the adult J. lalandii the Y-organ is about 8 mm long by 4 mm high, but even in immature specimens with a cephalothoracic length of 33 mm it is larger than that of either Orconectes or Carcinus and measures approximately 2-5 mm long by 0-75 mm wide. In the puerulus stage it is proportionally smaller, being about 310 to 370 p. long and 90 ^ wide in specimens having a cephalothoracic length of 9 mm. It seems to be less compact than that of Carcinus maenas (Passano, i960), and in surface view (fig. 75) has the appearance of whitish, convoluted ridges arranged in a slight crescent towards the posterior. Fig. 75. Surface view of left
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
