252 H. E. JORDAN 



The apparently unfortunate gap in the material between full 

 term and about eight months post-natal life leaves no serious 

 lacuna in the developmental history. The gland at term is in 

 all respects, save size, like the gland of the young animal. The 

 sole change is one of increase in bulk (ca. 5 diameters) due to 

 continued proliferation of the parenchymal cells and increase in the 

 amount of connective tissue and neuroglia framework. 



The order of description follows the order of development. Re- 

 garding stages prior to the 5 cm. phase, it may suffice to note that 

 the epiphysis is simply a shallow pocket lined with proliferating 

 epend^'mal cells more numerous apically. 



THE 5 CM. STAGE OF DEVELOPMENT 



At this stage the pineal pocket has taken a slight backward 

 direction. It communicates with the third ventricle through a 

 wide mouth, the pineal recess. It is invested by a very delicate 

 sheath of pia mater. The cells are more crowded around the 

 lumen and in the ventral wall, and here more closely resemble 

 the original ependymal ancestors. Distally and in the dorsal wall 

 the cells have become irregularly stellate or inultipolar for the 

 most part, and form a comparatively loose-meshed reticulum 

 (fig. 1). Very delicate fibrils are present, and about three cells 

 in every section contain small melanic granules. A number of 

 cells, including some with the melanic granules, are in mitosis. 

 Transition stages are abundant between true ependymal cells and 

 the differentiating stellate or neuroglia cells. The nuclei of the 

 latter are vesicular, with plasmosome and numerous karyosomes. 

 The cytoplasm is reticular. In the pineal body of this stage occur 

 the first steps in the differentiation process of ependyma into 

 neuroglia. No neuroblasts are recognizable. The neuroglia fibers 

 appear to arise from the spongioplasm by a process of thickening 

 and fusion. 



THE 10 CM. STAGE OF DEVELOPMENT 



The significant difference between the pineal body of this and 

 earlier stages is a slightly greater backward elongation, coincident 



