62 HENKY MCELDERRY KNOWER 



appendage to the body, well fitted by its greater length and 

 expanded fins for the increase in active feeding movements 

 observed at this time. 



With absorption of the yolk the digestive tract lengthens, 

 and a number of spiral coils are soon visible in the intestine, 

 resulting in enlargement of the round abdomen. The factors 

 at work in producing these changes, with their influence on 

 the lymphatic system, were outlined in my paper of 1908 

 (section 5, p. 60) as follows: 



' ' Though the early connections may be traced in older embryos, 

 the primary segmental arrangement is later obscured by the 

 increase in connective tissues, by the gradual growth and con- 

 centration of the pronephric sinus (ductus Cuvieri), by the 

 distention of the dorsal coelomic cavity, and by the consequent 

 shifting of the relations of the lymph hearts until they come 

 to lie above the posterior portion of the pronephros . . . ." 



This statement still holds true for the general picture, but the 

 details illustrated in figures 30 and 31 must be considered, to 

 appreciate the alterations in the lymphatic system and its new 

 relations in the body in this late larva (Pollister's late 23). 



ADJUSTMENTS OF LYMPHATICS TO BODY CHANGES IN 

 LATE TADPOLE FORM 



When the dorsal wall of the abdomen has been raised to 

 the level of the dorsal surfaces of the lateral muscles, the 

 larva presents a broad back to the view (fig. 31), and since 

 the lateral lymphatics have been carried along with the dorsal 

 wall, both lateral and dorsal vessels are now spread out on 

 the same plane, all appearing to belong to one dorsal system. 

 In this way even the large lymph trunks known from their 

 history to belong to the lateral system, might be mistaken for 

 dorsal vessels unless correction is made by comparison with 

 pictures of earlier stages (figs. 23, 26, etc.). 



