58 HENRY MCELDERRY KNOWER 



increase in the flow of lymph from behind with no new or 

 freer outlet provided, supporting this explanation. 



ASSUMPTION OF ROUNDED-UP, GLOBULAR, TADPOLE BODY 

 FORM AND DEVELOPMENT OF INTESTINAL COILS 



The main lymph ducts become adjusted to late body changes 



On turning from special consideration of the cephalic 

 sinuses to continue the account of the general development 

 of the lymphatics in later stages, the condition of the system 

 reached in stage 4 of the third period, and described in the 

 preceding pages (pp. 46-48) for figures 14 to 17, is followed by 

 a period of growth and differentiation, without sudden trans- 

 formations, through several successive stages, during which 

 the larva enlarges and acquires a marked disproportion be- 

 tween body and tail. The larva in figure 23 exhibits these new 

 proportions in its much lengthened tail with expanded fins, 

 now an organ more than twice the length of the body, which 

 has become a globular mass characteristic of late stages, by the 

 rounding up of the abdomen and head into an ovoid body. 

 In this mass the head is enlarged not only by the growth of 

 its organs and tissues, but by the added spacious cavity en- 

 closed within the operculum, which extends decidedly further 

 posteriorly. (It is still open.) How r ever, the changes which 

 produce the new globular shape in the body mass are largely 

 the result of a shifting in the position of the different sections 

 of the gastrointestinal canal, rather than growth of the head. 



Until after stage 4 (figs. 14 and 15) the digestive tract forms 

 a long cone-shaped mass which determines the shape of the 

 abdomen, with the base (stomach) of the cone forward, and 

 the apex tapering into the hind-gut, In the next three stages 

 (Liu-Li 4, 5, 6, '30; Pollister's early 23, '37), occupying only 

 a brief period, this elongated figure of the abdomen becomes 

 a shortened ovoid mass, by the rotation of the large yolk-filled 

 mid-gut into a new position across the axis of the abdomen. 

 In this movement, the junction of mid-gut with the hind-gut 

 is carried anteriorly and at the same time dorsally, the hind- 

 gut elongating and becoming fixed along the dorsal wall of 



