THE CONNECTIONS OF THE GONADIAL BLOOD VES- 

 SELS AND THE FORM OF THE NEPHRIDIA 

 IN THE ARENICOLIDyE. 



ELLIOT ROWLAND DOWNING, PH.D., 

 NORTHERN STATE NORMAL SCHOOL, MARQUETTE, MICHIGAN. 



The gonads of Arenicola occur on certain blood vessels that lie 

 diagonally on the exterior of the glandular portion of the nephridia 

 and that are consequently designated the gonadial vessels. In a 

 study of the gonads, the results of which will be published shortly, 

 it was found that the literature of the subject contained conflict- 

 ing and inaccurate statements regarding the relations of these 

 gonadial vessels to their connecting vessels. This paper is the 

 result of an attempt to determine these relations. 



Gamble and Ashworth, in 1900, published an extended study 

 of the anatomy of the several species which also reviewed the 

 important literature on the family. They had previously pub- 

 lished, 1898, a paper on the anatomy of Arenicola marina. In 

 an article published in 1899, V. Willem disagreed with some of 

 their statements as did R. Lillie in a more recent publication, 

 1906. These contradictory statements I shall try to adjust : I 

 must also take exception to some other statements of each. 



The general relations of the blood vessels may be easily un- 

 derstood from the accompanying partly diagrammatic figure of a 

 cross-section at about the level of the first nephridium of A. cris- 

 tata (Fig. i). It will be noted that there are two main blood 

 vessels, a dorsal and a ventral ; these run the entire length of the 

 animal. There is a pair of neurals of much smaller caliber, also 

 extending the full length of the body. The paired gastric lat- 

 erals and subintestinals, as also the paired integumentary vessels 

 known as the parietal (or dorsal longitudinal) and the longitudinal 

 nephridial, are limited in their extent and vary in length and 

 prominence in the several species. 



All previous authors agree in the arrangement of the nephridial 

 vessels as follows : The afferent vessel, on approaching the 



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