60 HENRY MCELDERRY KNOWER 



still be traced, though now the main afferent reception trunks 

 from in front and behind (figs. 27, 28) meet over the heart in 

 strong arched tubes (figs. 27, 28, 30; Dsl.R.D.). The junction 

 of the jugular lymphatic with the heart vessels is conspicuous 

 in figures 25 and 27, and the proximal end of the pericardial 

 tract is also shown as it joins the jugular lymphatic. The 

 temporal sinus of the jugular tract, dilated in the earlier 

 stages, is much enlarged as already explained in discussing 

 the cephalic sinuses (pp. 50-58). 



As in early stages, the dorsal lymphatics extend far forward 

 over the heart vessels, with which they connect from a plexus 

 much like that in previous figures (figs. 26, 27). The periph- 

 eral outgrowths of the dorsal trunk in the tail fins are now 

 more numerous, and have begun to branch. They are still 

 largely confined to the inner zone of the fins. Anteriorly, the 

 afferent vessels from over the ear and along the hind-brain 

 now branch freely, and anastomose to form the beginning of 

 the anterior section of the dorsal system characteristic of older 

 larvae, accessory to the original median dorsal plexus. 



The lateral lymphatics 



In this stage, continued posterior growth and a more habit- 

 ual use of the longitudinal paths have changed the pattern of 

 the lateral lymphatics from the irregular plexus of early 

 stages to a system in which the lateral line trunk and the 

 ventral lymphatics derived from the original lateral plexus 

 have become prominent, at the expense of short segmental 

 connecting elements of the plexus (figs. 26, 27). 



In figure 23 a large vessel running through the crowded 

 lateral plexus can be identified as the main lateral line lym- 

 phatic. The ventral lymphatic joins it in the plexus ante- 

 riorly, as in earlier stages. Similar relations are shown in 

 figures 26 and 27, in a more open plexus, where the connections 

 of the main lateral and ventral trunks are well exposed. 

 Afferent lymphatics entering the ventral and lateral trunks 

 from the abdominal wall already observed in stage 4 (fig. 15) 



