LYMPHATICS IN FROG LARVAE 55 



Comparison of the available injections indicates that when 

 the pressure is low and evenly balanced from front to back, 

 the injection normally reaches the pericardial duct from its 

 posterior connection with the jugular lymphatic and runs 

 forward to end blindly back of the central vessel of the area, 

 as appears in its early form in figure 20. A similar result is 

 exhibited in figure 21, L, with the dilated central sinus very 

 lightly injected and the pericardial duct with its small termi- 

 nal cavity evidently filled from behind, lying in contact with 

 the posterior wall without connection of the cavities. The 

 same conditions are exhibited in figure 22 for the later stage, 

 and the connections of the two sinuses are established still 

 later. 



Following their establishment, the submaxillary lymph 

 sinuses, like the temporal, increase in size and become dis- 

 tended, but the original form of the system and the relations 

 of the individual sinuses remain unaltered in later stages, as 

 is seen by comparing figure 21 with figure 22, drawn from a 

 12-mm. larva, the latest injection of this special region. 



A further series of special injections is not available to 

 illustrate the transition to the definitive form of the system, 

 shown in Hoyer's much older larva of 26 mm. (see pi. 10, 

 Hoyer, '05, fig. 3 of ventral view). The transition is, however, 

 evidently brought about by the fusion of certain sinuses; the 

 temporal and mandibular sinuses and the base of the circum- 

 oral lymphatic uniting at the sides, while the two mandibular 

 sacs fuse across the mid-ventral line to form a single large 

 cavity in front. The central sinuses form the transverse axis 

 of the system, as in earlier stages. They remain apart in the 

 mid-ventral zone, and each is joined posteriorly by the peri- 

 cardial sinus of its side. 



SUGGESTIONS AS TO CAUSE OF DEVELOPMENT OF CEPHALIC 

 SINUSES IN ANURA 



The cause of the expansion of the lymph sinuses in the head 

 of anuran larvae is not explained. Kampmeier attributes the 

 distention to accumulation of lymph in the early vessels of 



