. V//&///S Text-fig. 47. Pyura legumen (Lesson) (St. 57): A, intact specimen; B, test-spine; C, part of dorsal lamina. Pyura georgiana Michaelsen (St. MS 14): D, intact specimen; E, test-spine; F, part of dorsal lamina. Pyura bouvetensis (Michaelsen) (St. 181): G, intact specimen; H, test-spines; J, probable attitude in life with body resting lightly on the bottom. length to stalk length bears no direct relation to the total size of the animal, that is, to its age (see Text-fig. 48). Irregular longitudinal furrows mark the surface, and in some animals these break the test into rectangular
. V//&///S Text-fig. 47. Pyura legumen (Lesson) (St. 57): A, intact specimen; B, test-spine; C, part of dorsal lamina. Pyura georgiana Michaelsen (St. MS 14): D, intact specimen; E, test-spine; F, part of dorsal lamina. Pyura bouvetensis (Michaelsen) (St. 181): G, intact specimen; H, test-spines; J, probable attitude in life with body resting lightly on the bottom. length to stalk length bears no direct relation to the total size of the animal, that is, to its age (see Text-fig. 48). Irregular longitudinal furrows mark the surface, and in some animals these break the test into rectangular or polygonal areas each bearing a group of spines. The degree to which spines are developed is very variable. They may be numerous and short, forming a kind of fur, or few and scattered. When well developed the spines reach 2 mm. in length, are sharply pointed, and bear small thorn-like processes (Text-fig. 47 B). Atrial organs. The three pads, called atrial organs, which lie within the atrial siphon, at its base, have been noticed by several workers, especially Michaelsen (1900) and Arnback (1938). The structure and function of the organs, however, have never been clarified. Sections show that the atrial organs are thick pads of test substance richly provided with blood spaces. As these spaces are lined with
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