EMBRYONIC GROUND PLAN IN GANOIDS 19 



Allen was unable to determine the presence of any connection 

 between this structure and the veins in the adult fish. Allen 

 states as follows regarding this profundus facial trunk (page 47) : 



''The profundus facial trunk (figs. 4 and 5, P.Fac.L.V.) 

 could only be found in the orbit; branches were seen to enter it 

 from the adductor mandibulae muscles, and it was traced to a 

 point in front of the prootic foramen, where it probably passed 

 under the jugular and entered the abdominal sinus. This point, 

 however, could not be determined." 



The 'cephalic sinus' described by Allen in Scorpaenichthys 

 and the 'Kopf-Sinus' described by Jos. Hyrtl ('43) in the trout, 

 correspond to the medial pharyngeal lymphatic (4 in figs. 13 and 

 11) found in the embryos of ganoids and the trout. 



As the matter stands at present, considerable confusion would 

 necessarily arise if one attempted to homologize the lymphatics 

 as met with in the head and pharynx of adult ganoids and 

 teleosts. Since the conditions in the adult have been found, 

 in both cases, to be modifications of a common embryonic 

 ground-plan, I have deemed it expedient to apply a set of terms 

 to the lymphatics of the embryo which appear to be applicable 

 to them, and to which the chief vessels in the head and pharynx 

 of the adult can be uniformly referred. • 



What I take to be subocular lymph sacs are also met with in 

 the embryos of selachians. In a 50 mm. embryo of Mustelus 

 they were found to consist of exceedingly large semi-lunar shaped 

 structures filled with blood, closely opposed to the medial side of 

 the eyes, and to be in communication with the veins. A compari- 

 son of the subocular lymph sacs of fishes leads one to infer that 

 their primitive function was to drain directly into the veins in 

 the immediate vicinity of the sacs. It is seen that they function 

 in this manner even at a relatively late stage of development in 

 Mustelus and may possibly continue to do so in the adult; that 

 they communicate in the same manner with the veins in ganoids 

 during a short period of development; while in the trout and 

 possibly in other primitive teleosts, like the trout, no direct 

 communication is established between them and the veins, as in 

 selachians and ganoids, in the immediate vicinity of the sacs. 



