VARIATIONS IN RATE OF DEVELOPMENT 53 



the lateral pharyngeal lymphatic of the opposite side could not 

 be injected under pressure; in two embryos the lateral pharyngeal 

 lymphatic could be injected on both sides of the body, only as 

 far forward as the caudal end of the otocyst ; in one embryo the 

 lateral pharyngeal lymphatic could be injected on both sides of 

 the body as far forward as the subocular lymph sacs but did not 

 communicate with them; in one embryo the lateral pharyngeal 

 lymphatic could be injected only to the caudal end of the otocyst 

 on one side of the body, and to the anterior end of the otocyst 

 on the other. 



On the twenty-first day the following observations were made 

 upon thirteen {13) embryos: 



In five embryos the subocular lymph sacs could be injected on 

 both sides of the body through the lateral pharyngeal lymphatic ; 

 in six embryos the subocular lymph sac could be injected only on 

 one side of the body and, in each case, the lateral pharyngeal 

 lymphatic of the opposite side injected up to the sac but did not 

 communicate with it ; in one embryo the lateral pharyngeal lym- 

 phatic could be injected only as far forward as the caudal end 

 of the otocyst; in one embryo the lateral pharyngeal lymphatic 

 could be injected on both sides of the body as far forward as the 

 middle of the otocyst. 



On the twenty-second day both subocular lymph sacs could be 

 injected through the lateral pharyngeal lymphatic in almost 

 every case (about 90 per cent). Soon after the establishment 

 of a connection between the subocular lymph sac and the lateral 

 pharyngeal lymphatic, valves begin to be formed at the typical 

 points at which the lymphatics permanently communicate with 

 the veins. It then becomes more difficult to inject the lymphatics 

 from the veins without causing extravasations. 



I fully appreciate that the above-mentioned results apply to the 

 conditions found in relatively few embryos and that, in all proba- 

 bihty, the injection may not, in all cases, have been complete. 

 In view of the fact, however, that essentially similar observations 

 were made upon eight other separate occasions, I feel that they 

 represent, to a very fair extent, the conditions as they actually 

 exist. 



