Franklin P. Mall 341 



toward the action of pepsin. The action of pancreatin is in a measure 

 the opposite. 



Cartilage. 



Cartilage appears as a band of condensed tissue on either side of the 

 head of tadpoles just before the mouth breaks through. In the region 

 destined to become cartilage the nuclei of the connective-tissue syn- 

 cytium become first slightly enlarged, for nuclear figures are here more 

 numerous. The eudoplasm around the nuclei extends rapidly, and 

 due to the multiplication of nuclei now fills the entire space and partly 

 obscures the exoplasm of the syncytium. Where the endoplasm passes 

 over into the exoplasm there is now a sharp line of demarcation making 

 it appear as if the capsule of the cartilage cell were forming. 



In tadpoles about 6 mm. long, immediately after the mouth has 

 broken through, the nuclei of the precartilage are surrounded by a 

 solid mass of endoplasm, thus filling up all the space between them. 

 Where the nuclei are more separated the exoplasm is at the periphery 

 of the endoplasm, but where the nuclei are packed together the exo- 

 plasm is wholly obscured. The endoplasm stains quite intensely with 

 Congo red, not more so, however, than the protoplasm of other cells. 



A tadpole 9 mm. long has in it slender bands of cartilage fully devel- 

 oped from which the ground substance is directly continued into the 

 exoplasm of the surrounding syncytium (Fig. 7). The best pictures 

 are found at the tips of growing cartilage which are being added to 

 by a transformation of the neighboring syncytium. Where the border 

 of the cartilage is sharply defined the transition into the surrounding 

 tissue is not marked, for its boundary line is obscured by a layer of 

 flat cells. In a suitable specimen it is seen in passing from the syncy- 

 tium over into the cartilage that the nuclei gradually become more and 

 more crowded and the bundles of exoplasm become smaller and smaller. 

 The nuclei gradually come to lie in the meshes formed by this exo- 

 plasm, that is, they have been extruded from the syncytium. With this 

 change of relations between the nuclei and the exoplasm there is an in- 

 crease of the endoplasm which now fills the meshes, encroaches upon the 

 exoplasm, and partly obscures it. At this time the endoplasm of the 

 syncytium stains with congo red, but as the finished cartilage is ap- 

 proached, the nuclei and surrounding endoplasm are separated by deli- 

 cate lines or fibrils of exoplasm, which stain with hgematoxylin. These 

 lines now widen, stain more intensely with hgematoxylin, and form the 

 ground substance of the cartilage. The endoplasm becomes clearer 

 and clearer, separates from the ground substance, and finally encircles 



24 



