. Elements of Comparative Anatomy. . S92 COMPAEATIVE ANATOMY. evidently a compact germ-gland (Fig. 152, a), from which an efferent duct (6) passes off on each side. We find this arrangement of the germ-gland in the Branchiata, and in some of the Tracheata (Ar- achnida). In almost all the Crus- tacea the efferent duct is completely double as far as its orifice {A). The '^ ^ same arrangement obtains in the Mg is^i. Diagrams of the cliaractcrs Myriapoda, among the Tracheata. or the generative system lu the .,.,'' ^ -^ , ,9 . , -, -i • Arthropoda. a Germ-glauds. tcEffie- The germ-gland begms to be
. Elements of Comparative Anatomy. . S92 COMPAEATIVE ANATOMY. evidently a compact germ-gland (Fig. 152, a), from which an efferent duct (6) passes off on each side. We find this arrangement of the germ-gland in the Branchiata, and in some of the Tracheata (Ar- achnida). In almost all the Crus- tacea the efferent duct is completely double as far as its orifice {A). The '^ ^ same arrangement obtains in the Mg is^i. Diagrams of the cliaractcrs Myriapoda, among the Tracheata. or the generative system lu the .,.,'' ^ -^ , ,9 . , -, -i • Arthropoda. a Germ-glauds. tcEffie- The germ-gland begms to be dl- rent duct. vided among the Crustacea. The oro-an is then divided between its two efferent ducts (Insecta). The approximation of the orifices leads to the formation of a common orifice, and this to the forma- tion of an unpaired portion of the duct (c). In many Arachnida this azygos tract is connected with a circular part, more or less of which is formed by the germ-gland (0). The ring is then formed by an inherited (primary) stage—the single germ-gland—and by an acquired (secondary) stage—the fused part of the efferent ducts. While the generative glands of the Crustacea form the lowest grade of this series, the Insecta appear to form the highest, for, owing to the bilateral separation of the germ-gland, and the terminal fusion of the efferent ducts, and the formation of a common unpaired portion, they are the farthest removed from the lowest stage (D). The germ-glands, as well as the efferent ducts, may undergo various differentiations: especially the ducts, of which sometimes the paired and sometimes the unpaired portion is affected. Except in the fixed Cirripedia, impregnation is effected by copulation. In corre- spondence with this there is a space formed near to, or at some distance from, the terminal portion of the female efferent duct, from a diverticulum of a division of it; this (receptaculum seminis) serves to take up the sperm, and may be converted into a
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