Franklin P. Mall 331 



In very early embryos the mesenchyme is composed of individual cells 

 which increase rapidly in protoplasm and then unite to form a dense 

 syncytium. The protoplasm of the syncytium grows more rapidly than 

 the nuclei divide, so that in a short time we have an extensive syncy- 

 tium with a relatively small number of nuclei. In its form the syncy- 

 tium appears as large bands of protoplasm with spaces between them 

 filled at times with cells and at other times with fluid. The second 

 condition we have in the umbilical cord of young human embryos. 

 About this time the protoplasm of the syncytium differentiates into a 

 fibrillar part, which forms ihe main portion of- the syncytium— the 

 exoplasm — and a granular part, which surrounds the nucleus — the 

 endoplasm. The fibrils of the exoplasm are very delicate and anasto- 

 mose freely. When cartilage develops the exoplasm of the syncytium 

 becomes denser and denser; the nuclei and endoplasm wander into the 

 spaces of the exoplasm, which finally becomes semi-hyaline and takes 

 the characteristic stain of the ground substance of cartilage. Eeticulum 

 of the lymph node is easier studied, for here we have the least differ- 

 entiated form, although the pictures are not so^ striking as they are 

 in the development of cartilage. The development of the cornea is 

 intermediate between reticulum and white fibrous tissue. In the de- 

 velopment of membranous bone the process is similar to that of car- 

 tilage, only that the nuclei and endoplasm form the characteristic 

 osteoblasts a little earlier and the ground substance deposited in the 

 exoplasm does not stain with hgematoxylin. In the development of 

 white fibrous tissue the nucleus and endoplasm lie upon the bundles of 

 anastomosing exoplasm and in the course of time the anastomoses break 

 and the exoplasm splits to give rise to the individual fibrils of white 

 fibrous tissue. 



The study of the development of elastic tissue is less satisfactory, 

 usually, however, it develops in the middle of the exoplasm, the fibrils 

 being extremely delicate at first, and anastomose from the beginning. 

 Elastic tissue never develops by itself, but always in conjunction with 

 some collagenous tissue, embryonic or mature. 



Development of the Connective-Tissue Syncytium in the 



Tadpole. 



Through the kindness of Professor Harrison I am enabled to follow 

 the formation of the connective-tissue syncytium from the mesenchyme 

 in a set of perfect serial sections of the tadpole. The sections had all 

 been stained in hrematoxylin and congo red and were cut 7i n thick. 



