SEXUAL ORGANS IN THE PRIMITIVE VERTEBRATE. 26/ 



later period. We may, therefore, assume that the primitive 

 Vertebrate possessed both ovaries (Fig. 60, 61, e) and 

 testes (h). 



Fig. 61. — Transverse section throngh the ^ 



posterior part of the ideal Primitive Vertebrate : ^^_ ^__^1 ^ a? 



/, float; mr, spinal tube; x, notochorcl ; ms, /^^■'^^ffWwh^x^"^ 



muscles ; e, ovaries ; n, primitive kidney ducts ; jMI jillii^^^^l!^^ 



a, body -arteries ; d, intestine ; v, intestinal vein. f 



The sexual organs of Vertebrates 

 are most intimatelv connected with the ^^^^^^^^ 



primitive kidneys, two glands running 



along near the notochord, which, in the embryo, secrete the 

 urine, and in Fishes and Amphibia, remain permanently as 

 urinary organs.^"^ In higher Vertebrates, their place is taken 

 at a later period by the permanent kidneys, which arise 

 from the posterior portion of the primitive kidney ducts. 

 In their earliest and simplest form, the primitive kidneys 

 appear to be a pair of simple ducts, running along either 

 side of the notochord within the body-cavitj^, and having 

 openings at their posterior ends (Fig. 60, n). In this form 

 they yet appear transiently in the embryo of higher Verte- 

 brates, and permanently in the Worms. 



The organs which we have thus enumerated in a 

 general survey of the primitive Vertebrate, and have ex- 

 amined in relation to their characteristic positions, are 

 those parts of the organism which are repeated in all 

 Vertebrates without exception, m the same mutual rela- 

 tions, though they are modified in very various ways. We 

 have turned our attention principally to the transverse 

 section of the body (Fig. 54-56), because it shows most 



distinctly the peculiar relative positions of these organs. 

 20 



