The development of the urinogenital organs of the lamprey. 7 



Exoderm und vereinen sich mit der hohl werdenden Anlage des 

 Ganges." 



Shipley (1888), like Scott, derives the pronephros and its duct 

 from the mesoderm, but in a different manner: "The lumen of the 

 segmental duct becomes continuous with a groove in the parietal 

 peritoneum, lying near the angle where the somatopleure and splanchno- 

 pleure diverge. When this groove closes it leaves four or five openings, 

 which persist as the openings of the ciliated funnels." The tubules 

 are continuous at their bases "with a duct which soon becomes elong- 

 ated and coiled and ultimately joins the segmental duct". The pro- 

 nephros ultimately comes to lie inside the cardinal vein. "There is 

 only one glomerulus on each side, stretching each side of the ali- 

 mentary canal and extending through about the same space as the 

 glandular part of the kidney; it receives its blood by a single vessel 

 on each side directly from the aorta." Shipley found five ciliated 

 funnels in the majority of specimens. "The whole gland did not ex- 

 tend over a greater space than that occupied by three myomeres, 

 although in some cases the ciliated funnels, which were of some length, 

 overlapped into the fourth myomere." Shipley concluded from these 

 observations that the lamprey pronephros does not have a metameric 

 origin. 



Semon (1890) published on the pronephros of Ammocœtes a brief 

 note in which he attempted to show that this form has inner and 

 outer funnels comparable with those which he found in Ichthyophis. 

 He also attempted to show that there exists in Ammocœtes a pro- 

 nephric chamber like that of Amphibians. 



Goette's account (189U) of the development of the lamprey pro- 

 nephros is the most complete that has been published. The earliest 

 indication of the organ appears soon after the heart is laid down in 

 the embryo and consists of a groove-shaped evagination of the somato- 

 pleure just ventral to the mesenteric fold. This evagination which 

 grows forward till it reaches the branchial region and backward, but 

 more slowly, is the rudiment of the pronephros anteriorly and posteriorly 

 that of the pronephric duct. "Die Kopfniere selbst entsteht also früher 

 als der übrige Gang, dieser aber als eine unmittelbare und gleich- 

 zeitige Fortsetzung des ersteren." The rudiment of the pronephros is 

 soon converted into a deep pocket which grows up close to and just 

 outside of the mesenteric fold, and has at first only a single slit- 

 shaped opening into the body-cavity. During the growth of this 

 pocket the lips of its opening unite at one point, thus forming two 



