Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 180 COMPARATIVE ANATOMY. either extraordinarily long, or short and simple, or provided with diverticula. These cavities are known as uteri; for in them the egg is not only enclosed in its shell, but as a rule passes through the early stages of embryonic development. A diverticulum of the female excretory duct, which has generally the form of a stalked vesicle, receives the sperm during copulation. In some cases there is a second diverticulum also ; it serves apparently for the reception of
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 180 COMPARATIVE ANATOMY. either extraordinarily long, or short and simple, or provided with diverticula. These cavities are known as uteri; for in them the egg is not only enclosed in its shell, but as a rule passes through the early stages of embryonic development. A diverticulum of the female excretory duct, which has generally the form of a stalked vesicle, receives the sperm during copulation. In some cases there is a second diverticulum also ; it serves apparently for the reception of the male organ (Bursa copulatrix). The most important complications of this system are seen in the parasitic Platyhelminthes. The preservation of the species is here subject to innumerable difficulties, owing to the animal living in different hosts at different stages of development, and to the wanderings which this mode of life entails; consequently a large number of ova have to be produced, and the certainty of fecundation insured. 148. The more special characters of this generative system exhibit extraordinary variation. The male portion has, in most Turbellaria rhabdoccela, the form of two elongated testicular tubes, from each of which a vas deferens is given off (Fig. 85, t). In the Trematoda, also, the testicles are, as a rule, but few, and rounded or lobate; these are represented in the Tur- bellaria dendrococla, as well as in several rhabdoccela (Macrostoma), and Cestoda by a number, and often a very large number, of small follicles, scattered in the parenchyma of the body (Fig. 86, t) ; these are connected together by long efferent ducts. They may form a single row on either side (land Pla- narians). The excretory ducts either form a common vas deferens, or each passes sepa- rately to a terminal portion, which is con- tinued into the copulatory organ. The common excretory duct forms the seminal vesicle, or, as happens in a few cases, it is formed by enlargements of th
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