SEXUAL ORGANS IN THE PRIMITIVE VERTEBRATE. 267 



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

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



testes Qi). 



FIG. 61. Transverse section through the 

 posterior part of the ideal Primitive Vertebrate : 

 /, float; mr, spinal tube; x, notochord; ms, 

 muscles ; e, ovaries ; n, primitive kidney ducts ; 

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



The sexual organs of Vertebrates 

 are most intimately 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. 87 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-cavity, and having 

 openings at their posterior ends (Fig. 60, ri). 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, in 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. 



