94 VERTEBRATES WITHOUT JAWS iv. 8 



The region that gives rise to the kidney during development lies 

 between the dorsal scleromyotome and the more ventral lateral plate 



card v 



glom 



on. t 



oes. 



pron. F 



Fig. 59. Section through newly hatched larvae of Lampetia hehind the pharynx. 



ao. aorta; card.v. cardinal vein; glom. glomerulus; fit. heart; my. myotome; n.c. nerve-cord; 

 not. notochord, which has collapsed because of lack of turbidity after fixation; oes. oeso- 

 phagus; pron.f. ciliated funnel of pronephros; pron.t. twisted pronephric tubule; sp. space 



around nerve-cord. 



Fig. 60. Kidney system of a 22-millimetre larva of Lampetra. 



tnes. mesonephric tubules; mesg!. mesonephric glomeruli; pr. pronephric funnels; 

 prd. pronephric duct; prgl. pronephric glomeruli. (After Wheeler.) 



mesoderm; it is known as the nephrotome. This tissue differentiates 

 during development from in front backwards, making a series of 

 segmental funnels, opening into a common archinephric duct (Fig. 

 58). The most anterior funnels open into the pericardium; usually 

 there are four of these in a freshly hatched larva, opening into a single 



