4 WILLIAM F. ALLEN 



Concerning the phylogeny of the lymphatics, Favaro and I 

 have shown that considerable anatomical data supports the hypo- 

 thesis that the lymphatic system of the higher or more special- 

 ized orders of fishes have their homologuo in veins in the lower or 

 more generalized orders of fishes. 



BLOOD-VASCULAR SUPPLY FOR THE TAIL-REGION 



To a\'oid confusion it may be well to consider first the distri- 

 bution of the blood vessels before taking up the lymphatics. 



Caudal artery. — As in other fishes the caudal artery in Scor- 

 pa^nichthys (figs. 4, 5, 7-10, C.A.) traverses the haemal canal di- 

 rectly below the centra. This trunk was also seen in nearly all 

 the transverse sections of Clinocottus. In these sections it should 

 not, however, be confused wdth the minor caudal artery with 

 which it runs parallel and is a branch. Beneath the last verte- 

 bra the caudal artery separates into a major and a minor fork. 

 Sometimes the main stem is the left fork, but more often it is the 

 right. The minor stem (figs. 9 and 10, R.C.A.) supplies the 

 musculature of the side of the fin; while the major stem or caudal 

 artery proper (figs. 4-8, 10, and 11, C.A.) continues caudad in the 

 space between the two hypural bones to the posterior ends of 

 these bones, where it bifurcates to form a dorsal and a ventral 

 caudal fin artery. Immediately behind the last vertebra the 

 posterior neural artery (figs. 6 and 7, P.Neu.A.) is given off from 

 the major stem of the caudal artery to pass dorsad in a median 

 line, a little in front of the superior hypural bone. In the speci- 

 men from which fig. 7 was drawn it passed across the base of the 

 left side of the superior hypural and along the left side of the 

 last interspinal bones to break up in a deep network in the con- 

 nective tissue covering these bones, but in most of the other dis- 

 sections it had a similar course on the opposite or right side. A 

 little caudad of the last vertebra a pair of hypural arteries (figs. 

 4-7, Hyp. A.) are sent off to either side of the superior hypural 

 bone, which they cross obliquely and break up in a capillary net 

 work on the posterior and dorsal surfaces of the bone. These 

 arteries may have arisen from the fusion of several of the embry- 



