22 UNITED STATES NATIONAL MUSEUM BULLETIN 296 



detail: Trypetesa lampas, Cryptophialus minutus, Lithoglyptes indicus, 

 and Bemdtia purpurea. The maxillary glands are located on both sides 

 just posterior to the mouth, with portions extending anteriorly into 

 the second maxillae and posteriorly along the ventral thorax. Three 

 paired parts have been described: the endosac, urinary bladder, and 

 urinary duct. The endosacs lie immediately posterior to the second 

 maxillae, are slightly swoUen, and contain a large and usually dark- 

 colored globular mass. It is generally assumed that this portion serves 

 the main excretory function. The paired urinary bladders are situated 

 anteromedially from the endosacs, to which they are connected by a 

 narrow funnel, and are often triangular in shape. The urinary ducts 

 are small and thin-waUed, and are difficult to foUow in serial sections. 

 They open on the second maxillae. 



Utinomi (1960, p. 21) refers to cephalic nephrocytes in Bemdtia 

 purpurea. These are extremely large and round cells in numerous 

 masses scattered through the cephalic region. He proposes that these 

 may be another sort of excretory organ. Other similar cells are found 

 scattered throughout most of the rest of the body. All resemble the 

 cells containing carmine following injection experiments conducted 

 on other Crustacea. No injection experiments are known for acro- 

 thoracicans, however. Feeding fine carbon particles to Trypetesa 

 lateralis (see page 20) gave no indication of phagocytosis of ingested 

 particles. 



The function of the maxiUary glands probably is to remove cellular 

 wastes flowing through the blood lacunae scattered throughout the 

 body and mantle, and may be supplemented by the nephrocytes and 

 digestive glands. 



Muscular System 



The muscular system of the acrothoracicans has been studied in 

 detail and in a comparative manner by Utinomi (1960). Much of the 

 summary below wUl be following the terminology of Utinomi, who in 

 turn follows Nussbaum's (1890) work on thoracicans. 



The mantle contains two layers of muscle, one longitudinal and one 

 radiating from the attachment area in a generally circular manner. 

 Typically the longitudinal strands are external, but these may inter- 

 lace in a complex manner. These discreet longitudinal muscle bands 

 terminate somewhat short of the mantle aperture — the only mantle 

 area lacking two sets of muscle strands. Additional muscle bundles of 

 special function may radiate from the area of the horny knob or upper 

 end of the attachment disk, especially in species bearing lateral bars, 

 to reinforce the support of the mantle during body movement and 

 abrasive mantle activity. 



