546 PHOP. a. B. HOWES ok some 



It is interesting, in view of this and in its possible bearing 

 upon the ancestry of the Chordata, to recall the fact * that the 

 Ttmicata, unlike the higher hermaptroditic Chordata, are mostly 

 pro togy nous. 



III. That the genital ducts of adult Teleosteans, when present, 

 are invariably continuous either with the membranes which 

 suspend the genital glands or (most modified term) with those 

 which invest them, is well known. They are frequently paired, 

 becoming median and unpaired only when the glands are, as in 

 the female Cod, united and saccular. The steps in the realization 

 of this continuity have been worked out by Jungersen f and 

 others. The urino-genital organs of the Teleostei diifer col- 

 lectively from those of all other Vertebrates, with the exception of 

 the Q-anoidei and MarsipobrancTiii, in the absence of undoubted 

 vestiges of the genital ducts of the opposite sex. 



Balfour, in dealing, at the end of his career, with the develop- 

 ment of the urino-genital system of the Yertebrata generally, laid 

 it down as his final conclusion % that the ducts of the Teleostei are 

 most probably " in both sexes . . . modified Miillerian ducts" (cf. 

 I. c. p. 606) ; and he further pointed out that while analogy 

 would suggest that they might (p. 580) " correspond with the 

 Miillerian ducts of Elasmobranchii," &c., on this point there was 

 " no positive embryological evidence." Balfour was contending 

 for his belief in the homology of the "Miillerian ducts" through- 

 out the Vertebrata, as tubes formed in relation to the head 

 kidney and to a splitting of the segmental ducts §. The tendency 

 of post-Balfourian investigation into the morphology of the ver- 

 tebrate urino-genital system has been towards the overthrow of 

 this conception ; and, indeed, with the recent discoveries of Yan 

 Wijhe II, Marshall and Bles IF, and others named on the next page, 

 the Elasmobranchii occupy a well nigh isolated position as the 

 only great group of Yertebrata for which it has not been either 



* Cf. Herdman in ' Challenger ' Eeports, vol. xiv. Tunicata, p. 23. 

 1- Loc. cit. p. 179. 



I Oomp. Embryology, vol. ii. p. 605. 



§ Cf. Sedgwick, Quart. Journ. Micr. Soi. n. s. vol. xxi. p. 468 (1881). 



II Archiv f. mikr. Anat. Bd. xxxiii. p. 461 (1889). 



^ Studies Biol. Lab. Owens OoU. Manchester, vol. ii. p. 185 (1890). 



