Franklin P. Mall 353 



The whole node is composed of a delicate syncj'^tium which now shows 

 all of the characteristics of a fnliy developed reticulum, with many 

 nuclei and endoplasm lying upon it. The meshes are partly filled with 

 lymph cells. At the surface of the node the reticulum is continuous 

 with the syncytium of the surrounding tissue. That there is a contin- 

 uous network is best seen in sections stained by Mallory's method, 

 which also show that the meshes are smaller and the fibrils are more 

 delicate than those of the surrounding syncytium. 



" The node has grown to be 3 mm. in diameter in embryos 20 cm. 

 long. Each node is now surrounded with a delicate capsule of prefi- 

 brous tissue, and the reticulum, prefibrous tissue and surrounding syn- 

 cytium form one continuous network. Upon the reticulum there are 

 but few spindle cells and within the meshes there are many lymph cells." 



From the above description it is seen that the reticulum develops 

 directly from the exoplasm of the syncytium, while the nuclei and 

 endoplasm are converted into cells which' lie upon the reticulum fibrils. 

 After the node is outlined the surrounding syncytium develops into 

 prefibrous tissue to form the capsule. 



The study of sections of the pig's intestine stained by Mallory's 

 method shows definitely that both white fibrous tissue and reticulum 

 are developed directly from the syncytium lying between the muscle 

 wall and the epithelium. In embryos 20 cm. long there are small villi 

 and rudimentary crypts present, but there is no marked muscularis 

 muscosfB to separate the submucosa from the mucosa. There is no 

 line of demarcation between the reticulum of the mucosa and the white 

 fibrous tissue of the submucosa, more than a few scattered muscle cells 

 of the muscularis mucosae. The tissue around the bases of the embry- 

 onic crypts is fibrillated, wavy, and generally parallel with the muscu- 

 laris mucosa3, stains more intensely and corresponds with the prefibrous 

 tissue found elsewhere. From this layer there are gradual gradations 

 towards reticulum in the villi on one side to a less developed white 

 fibrous tissue in the submucosa ou the other side. The degree of devel- 

 opment of the layer of prefibrous tissue of the intestine is about the 

 same as that of the skin of the same embryo. 



The results here given suggest very much that reticulum represents 

 an embryonic form of white fibrous tissue. That these two tissues blend 

 and arise from a common syncytium does not speak for their identity 

 any more than it does for the identity of either cartilage or bone with 

 white fibrous tissue. As the matter now stands all of these tissues, 

 including that of the cornea, are to be classed as collagenous, but still 

 as distinct tissues. I have recently given the reasons for classing 



