THE PRONEPHRIC DUCT IN ELASMOBRANCHS 



GEORGE A. BATES 



From the Tufts College Medical School 



SIXTY-ONE FIGURES (fIVE PLATES) 



HISTORICAL RESUME 



The development of the pronephric duct in elasmobranchs 

 has been studied by a number of observers, with very different 

 conclusions as to its origin. These differences have arisen, in 

 part, from the difficulty of demonstrating cell boundaries and 

 limiting membranes in embryos preserved by the usual methods 

 and, in part, from the difficulty of interpreting oblique sections. 

 The theory that the vertebrates stand in phylogenetic relations 

 with the annelids and the consequent attempt to homologize 

 the nephridial system of the two is, in a measure, responsible for 

 the discussion and the resulting conflict of opinions. The question 

 in controversy is: Whether the duct takes its origin in whole or 

 in part from the mesoderm, or whether it arises from or is con- 

 tributed to by the ectoderm. At first there seems to have been 

 no hesitancy in pronouncing the origin to be entirely mesodermic^ 

 and all the early papers (Semper, et al) so described it. 



In 1888 Johannes Ruckert ('88) stated that "the duct is de- 

 veloped (in the group) from the ectoderm." Van Wijhe ('89) 

 claimed to have found evidence for the same conclusion. Several 

 papers followed in rapid succession describing similar conditions 

 in other groups; one author comparing the growth of the duct to 

 that of the lateral line nerve which, he claimed, is developed from 

 the ectoderm in the same way as the pronephric duct. The ques- 

 tion raised by such comparison has been answered by Harrison 

 ('03, '10). Within more recent years the statements have been 

 very conflicting, some stating that it is, at least in part, ectodermal 



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JOURNAL OF MORPHOLOGY, VOL. 25, NO. 2 



