80 OTTO F. KAMPMEIER 
In embryos, approximately 10 or 11 mm. long, the primary 
maxillary sinus acquires an outlet. The posterior extremity of 
the temporal division by further backward prolongation (figs. 34 
and 35) becomes confluent with the jugular lymphatic, which in 
turn gains access to the anterior lymph heart and conveys thither 
the lymph collected by the sinus. 
During the later larval and metamorphic periods, the primary 
maxillary sinus, as well as the other lymph channels laid down 
in the embryo, are converted into the superficial and deep lymph 
saes found in the adult.!°. Such changes will be reserved for a 
later paper. 
From the foregoing account of the appearance and relations of 
the early adherent anlagen of the primary maxillary lymph sinus, 
reinforced by the evidence of the photomicrographs illustrating 
it, the conclusion is forced upon one that they are probably deriva- 
tives by proliferation from the walls of the external jugular 
components of the early unspecialized jugulocarotid vascular 
plexus. Formerly (15) I believed that these observations 
afforded fairly decisive evidence in favor of the origin of lym- 
phatics from venous epithelium, and I suggested tentatively that 
certain discontinuous mesenchymal spaces of Amniotes, which 
had been described previously as incipient lymphatics, might 
have been derived early from neighboring blood channels in a 
manner hardly perceptible on account of the absence of any 
special differential characteristic in either the vascular intima or 
the mesenchyme. But after investigating more thoroughly other 
lymphatic channels in anuran embryos, as well as considering the 
evidence contained in the mass of literature which has accumu- 
lated in recent years on the problem of vasculogenesis, that opin- 
0 In The Anatomical Record, vol. 16, 1919, the writer stated that topograph- 
ical relations and genetic data show the primary maxillary lymph sinus of anuran 
tadpoles to correspond to the subocular lymph sinus of fishes. Since then I have 
carried on a comparative study of the lymphatic system in the different classes 
of vertebrates, and the available data force me to modify that statement. Pos- 
sibly only the dorsal lateral extensions of the principal portion of the primary 
maxillary sinus are concerned in the homology. Further observations bearing 
on this question will be considered in the comparative anatomy of the lymphatic 
system which is in process of preparation. 
