268 H. E. JORDAN 



2. At the 5 cm. stage the cells of the distal and dorsal walls have 

 become stellate with anastomosing processes forming a loose- 

 meshed syncytial network. This represents the first stage in the 

 formation of the neuroglia framework. The nuclei of the cells 

 are vesicular, wdth plasmosome and scattered chromatin granules. 

 The cj^toplasm is homogeneous or reticular (with occasional 

 vacuoles). A few of the cells contain a few melanoid (melanic) 

 granules. 



3. The body takes a backward direction in growth. The 

 apical cells proliferate more actively, thus forming a rounded 

 dome-shaped body with shallow proximal pineal recess continuous 

 with the third ventricle. Blind alveoli (cysts) make their ap- 

 pearance. The pia mater sends in vascular trabeculae dividing 

 the body into more or less distinct lobules and follicular compart- 

 ments of parenchymal cells. 



4. These same processes continue to half term (21 cm.) when 

 proliferation seems most active. The pigment granules are now 

 most abundant, and the 'alveoli' are largest and most numerous. 



5. Pineal bodies at birth are similar to the above, only larger. 

 There are besides, follicular collections of cells with central vas- 

 cular trabecula or capillary network, surrounded by a wide peri- 

 vascular lymph-space. 



6. Between birth and the end of the first year the pineal body 

 enlarges approximately five-fold. The pigment granules have 

 been distributed by mitosis of the containing cells among many 

 descendants thus giving the impression of a numerical decrease. 

 Vascular follicles are abundant. An occasional cyst remains. 

 Medullated nerve fibers can be traced into the basal portion and 

 in relation to the blood-vessels. The parenchyma consists of a 

 single cell type; a more (neuroglia cell and fibers) or less (inter- 

 neuroglia — spherical or polygonal) differentiated ependymal cell. 

 The cysts have disappeared in consequence of crowding of the 

 proliferating enveloping cells. 



7. After the first year local signs of degeneration appear, i.e., 

 increase of connective tissue and neuroglia, and the appearance 

 of brain-sand, large clumps of pigment granules, cell-free areas 

 of oedentatious neuroglia network, and a decrease of parenchymal 

 cells. 



