. Elements of Comparative Anatomy. 604 COMPAEATIVE ANATOMY. Petromyzontes it is first connected witli the one on the opposite side, to form an unpaired and wider portion. We do not yet know its relation to the metameric ciliated infundibula. In the Selachii the primitive arrangement is limited to the early stages of development. The primitive kidney extends along the dorsal wall of the coelom, and is made up of separate canaliculi, which commence by ciliated infundibula (Fig. 344, ?'), which open into the abdominal cavity. Each canal, after having broken up so as to en- close a glomerulus {m),
. Elements of Comparative Anatomy. 604 COMPAEATIVE ANATOMY. Petromyzontes it is first connected witli the one on the opposite side, to form an unpaired and wider portion. We do not yet know its relation to the metameric ciliated infundibula. In the Selachii the primitive arrangement is limited to the early stages of development. The primitive kidney extends along the dorsal wall of the coelom, and is made up of separate canaliculi, which commence by ciliated infundibula (Fig. 344, ?'), which open into the abdominal cavity. Each canal, after having broken up so as to en- close a glomerulus {m), is continued on into the archinephric duct. These canals increase in length, so that each of them forms a coiled lobule (r); each kidney, therefore, is composed of a series of these coils, which are col- lected together into the archinephric duct (tt). This duct opens into the cloaca. Changes may occur in the glandular portion of these kidneys, as well as in their efferent ducts. The anterior portion, which is made up of ^-;?=r77—-===5:^^/3 a number of lobules, does not undergo ^/ I ^SJ5^ '• any very great development, as does part of the hinder portion. This, which is made up of a varying, but large number of primitive lobules (13-14 in Acanthias), is converted into a larger organ, the canaliculi in which may be seen to increase in number by budding off new ones. This portion retains its renal function, while the anterior part is atrophied, and, in the male, enters into con- nection with the generative gland. The ciliated funnels (nephrostomata) are retained in some Sharks only; they disappear in all the Eays, and many of the Sharks. Where they are retained they are reduced in number. Of the changes which obtain in the primary archinephric duct the most important is its division into two parts. This commences at its anterior end, and extends backwards, so that there come to be two canals. One commences at the anterior abdominal orifice of the primary duct, and has no furt
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