24 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



Having considered the development of the subocular lymph 

 sacs of the trout, as far as can be observed by following the course 

 of the injecta in the living embryo, let us now turn our attention 

 to their study by means of sections. 



The embryos were fixed in aceto-sublimate, picro-sublimate, 

 Zenker's and Tellyesnickzky's fluids, all of which gave good re- 

 sults. Transverse, frontal and sagittal sections were studied, 

 ranging in thickness from six to twenty micra. The sections 

 were stained in borax carmine, Delafield's hematoxylin, Ehrlich's 

 hematoxylin, Delafield's hematoxylin-orange G, Delafield's hema- 

 toxylin-eosin, and Mann's methyl blue-eosin, as recently modi- 

 fied by Reagan ('14). The last-mentioned stain is especially 

 favorable for the demonstration of endothehum. 



It has already been mentioned on a preceding page that the 

 rate at which the lymphatic system develops depends largely upon 

 the temperature of the water in which development takes place. 

 Such being the case, it is evident, even for the same species of 

 trout, that a particular stage of development cannot be uniformly 

 designated as occurring upon any particular day. Even when 

 developed under the same conditions of temperature individual 

 variations are also of frequent occurrence; not only among dif- 

 ferent individuals of the same age, but even upon opposite sides 

 of the same individual. When the age of an embryo is men- 

 tioned in the following pages, it must not be regarded, therefore, 

 as uniformly related, in all cases, to the degree of development to 

 which it is assigned. 



The progressive increase in size which the subocular lymph sacs 

 of the trout undergo during the course of development is shown 

 in the series of reconstructions illustrated by figures 1 to 10, in- 

 clusive. These figures also show the independent character of the 

 subocular lymph sacs (1, figs. 1 to 9, inclusive) during the early 

 stages of development, and the connection which they second- 

 arily estabhsh with the lateral pharyngeal lymphatic (fig. 10). 



The earliest stages in the development of the subocular lymph 

 sacs, as observed in sections, are shown in figures 19, 20, 21, 22 

 and 23, which are photomicrographs of sections (10 micra in 

 thickness) that pass through the region occupied by the anlagen 



