In the abdomen it is surrounded by a large gland, the so-called liver, and is dilated at one spot (Fig. 186) to receive the ducts from this gland. The fluid elaborated by this large abdominal gland has been shown to have more affinity with pancreatic juice than with bile. The =Proctodaeum= consists of a short rectum, from the dorsal side of which protrudes a large sac, the “stercoral pocket.” At its origin, the rectum receives the openings of two lateral tubes which reach it after ramifying in the substance of the liver. These have been called “Malpighian tubules,” but their function is unknown. Loman[263] has shown that they open into the mid-gut and not into the rectum, and there is reason to believe that true Malpighian tubules homologous to those of Insecta are absent in Arachnida, where their place seems to be taken by the coxal glands, which are considered to be the true excretory organs. In most spiders they open near the third coxae. Like the stomodaeum, the proctodaeum has a chitinous lining. =Vascular System.=—The earlier investigations on the circulation of the blood in Spiders were made by direct observations of the movements of the blood corpuscles through the more or less transparent integuments of the newly-hatched young. Claparède’s[264] results were arrived at by this method. It is invaluable for demonstrating roughly the course taken by the blood, but in these immature spiders the blood-system has not attained its full complexity, and other methods of research have shown the spider to possess a much more elaborate vascular system than was at first suspected.