376 DENDRITIC APPENDAGE OF UROGENITAL PAPILLA 



in proportion to the urterial system as well as to the appendage itself. 



The nerves are supplied to the appendage from a pair of 

 spinal nerves sent out from the first caudal vertebra (Fig. 10). These 

 spinal nerves give near the root of the appendage one branch on each 

 side of the body which enters directly into the appendage and in- 

 nervates it. They run similar courses to the arteries but begin to 

 branch sooner th;in the latter. I have been unable to trace these 

 bundles into their final twigs, but I have recognised them in sections 

 near the tips of the lobes (Fig. 17). 



Besides these blood-vessels and nerves there is observed in the 

 inner zone of the appendage still another system of cavities, i.e., that of 

 the ill-defined lymph-cavities (Figs. 13-16). In serial sections it can 

 be traced in the body proper to the dorso-median lymph-cavity sur- 

 roundino- the aorta and the cardinal vein. JSTear the base of the stalk 

 (Figs. 13 îind 14), it may be branched into a pair or be simple, but on 

 its further course, (Figs. 15 and 16) it sends out here and there several 

 irregularly shaped branches. It is bounded by an endothelial mem- 

 brane while it passes through the connective tissue of the body proper, 

 but in the appendage from the base of the stalk upwards, there exists 

 no lono'cr a definitive boundary. Owiuü: to this circumstance, the 

 cavities have often collapsed by bad treatment and the lymph- 

 cavity appears then as if it ended blindly near the root of the stalk. It 

 can be traced for a certain distance towards the lobes of the appendage 

 but in the latter it vanishes in the loose fibrous tissue. 



All these structures of the corium are equally well observed in 

 various younger stnges. Even in such a stage as is represented in Fig. 

 8, there are already recognisable in the cross-sections of the stalk a pair 

 of arteries, a vein of considerable size, and a 13'mph-cavity of suitable 

 proportion in the same relations with one another as in the adult 

 (Fig. 12). The only noteworthy peculiarities of such a stage are the 



