353 The Development of the Connective Tissues 



endoplasm becomes larger, the exoplasm increases absolutely and rela- 

 tively in quantity. The nuclei and endoplasm form the well-known 

 bipolar cells, the tips of which rvm into and are lost in the exoplasm, ■» 

 making it appear as if the exoplasm were spinning its fibrils from the 

 granular endoplasm. Soon the fibrillated exoplasm is drawn out into- 

 bundles, the bands between them beginning to break, thus forming 

 the prefibrous tissue. The process of drawing out continues and the 

 prefibrous tissue is changed into embryonic white fibers, which at first 

 are irregular in size and anastomose occasionally. In the further de- 

 velopment the bridges break and the thicker fibers split into the indi- 

 vidual fibrils of white fibrous tissue. 



The first white fibers apjDcar in the perimysium, then they, grow as 

 radiations into the superficial fascia and cutis. Not only do the nuclei 

 of the syncytium multiply, but the exoplasm increases much out of 

 proportion. This continues in the prefibrous and embryonic fibrous 

 tissues by stretching, widening, and splitting the individual fibrils. 



Eeticulum. 



The reticulum of the 13'mph node is developed directly from the 

 connective-tissue syncytium, and is probably the least differentiated of 

 the connective tissues. This view has been advanced by writers, most 

 recently by Waldeyer. In its differentiation it begins much like white 

 fibrous tissue and when fully developed is about as far advanced as the 

 tissue I have termed prefibrous. When white fibrous tissue and retic- 

 ulum develop side by side it is impossible to separate them in their 

 early stages, but when the early development of the perimysium is 

 compared with the develojjment of reticulum of a lymph node it is 

 noticed that the arrangement of the fibrils is different, although their 

 development is parallel. In the liver the reticulum develops from 

 Kupffer's cells. 



The development of rhe reticulum of the lymph node is now under 

 investigation by Dr. Sabin who has given me the following resume with 

 the permission to publish it. " The lymph node has just appeared as a 

 plexiform mass of lymph ducts in embryo pigs 4 cm. long. These duets 

 can be injected from more distant lymph channels and within the node 

 they are relatively large and are separated from one another by bridges 

 of tissue, or primitive lymph cords. The lymph cords are composed of 

 a syncytium of delicate bands of exoplasm, with oval nuclei sur- 

 rounded by spindle-shaped endoplasm. In addition there are many 

 round cells which lie in the meshes — the first lymph cells. By the time 

 the embryo is 10 cm. long the lymph node is one millimeter in diameter.. 



