Franklin P. Mall 343 



nuclei somewhat larger with numerous karyokinetic figures. In the 

 neighborhood of the chorda the exoplasm of the syncytium is so dense 

 that it appears as a granular mass between the nuclei. The sheath of 

 the chorda is stained intensely blue. The endoplasm which is quite 

 marked around the nuclei of the syncytium near the spinal cord gradu- 

 ally disappears as the chorda is approached. By most methods of har- 

 dening the nuclei of the precartilage become so packed that the exo- 

 plasm of the syncytium is entirely obscured. Especially is this true 

 in the development of the cartilage of the arm. In an embryo pig, 12 

 mm. long, which had been macerated in Miiller's fluid for 24 hours, 

 washed in water, then in alcohol, stained in hiematoxylin and congo red, 

 the precartilage of the arm could also be analyzed. The nuclei of the 

 precartilage are all surrounded with a continvious mass of protoplasm, 

 stained red, which is directly continuous with the exoplasm of the 

 neighboring connective-tissue syncytium. In specimens which have 

 been macerated it is very difficult to separate the endoplasui from the 

 exoplasm of the syncytium. Therefore between the nuclei there is one 

 continuous mass of protoplasm practically of the same structure. 



In pigs' embryos from 15 to 20 mm. long the cartilages of the verte- 

 bral bodies are well developed and are pretty sharply defined. In 

 sections treated with Mallory's stain it is found that on the dorsal 

 side of the bodies of the vertebrae the ground substance of the cartilage 

 is directly continuous Avith the exoplasm of the connective-tissue syncy- 

 tium. By all odds the best place to study the early development of 

 the cartilage is in the occipital cartilages, which lie on either side of the 

 dorsal middle line. At this time the exoplasm of the connective-tissue 

 syncytium in the region of the occipital precartilage is in the form of 

 sharpened bands encircling definite openings, some of which contain 

 nuclei (Fig. 8). 



In a pig's embryo a little over 2 cm. long the main cartilages of the 

 body are all well developed, and in this specimen we obtain the best pic- 

 tures showing the relation of cartilage to the connective-tissue syncy- 

 tium. Again, the occipital cartilage shows all the transitional stages 

 from the completed ground substance to the exoplasm of the syncytium 

 (Fig. 10). Passing from the ectoderm of the embryo towards the car- 

 tilage it is seen that the main spaces between the exoplasm of the syn- 

 cytium become gradually smaller and smaller, with the nuclei shifting 

 into them as the cartilage is approached. This takes place before any 

 true ground substance is deposited, as the figure shows. Next we reach 

 a zone in which the exoplasm has ground substance deposited between 



