DEVELOPMENT AND IMMATURE STAGES. 177 



by the division of the cells of the wall ; the two lumina 

 soon communicate. The cells of which the mass is 

 formed before the lumen commences are large and 

 pyriform, having the smaller end turned toward the 

 axis of the cylinder ; their larger rounded ends pro- 

 trude beyond the cell-mass; their nuclei are large, 

 round, central, and stain deeply ; their contents are 

 clear, transparent, and non-absorbative. Later on, 

 when the lumen has enlarged greatly, the cells flatten ; 

 and their contents become finely granular and stain 

 easily. 



A similar process of development is found in the 

 more dorsally situated cellular papilla whence the large 

 globular gland arises ; after this has attained to a 

 certain size the pyriform cell-mass shows a vertical split, 

 which increases continuously ; the short, thin stalk by 

 which the body of the gland is fastened to the under- 

 lying parts remains solid for a long time. 



While these glands are growing the structure of the 

 testes undergoes considerable alteration ; hitherto they 

 have consisted of small indifferent cells not dis- 

 tinguishable from those of the female organs; now a 

 zone of small cells collects at the posterior pole and 

 there forms a spermatogenetic region. The outline 

 and the nuclei become clearly denned, and the cell-con- 

 tents stain more easily. The anterior portions of the 

 testes are already filled with spermatoblasts ; the vasa 

 deferentia acquire a lumen and are clothed with small, 

 cubical, epithelial cells. 



The changes which the testes and their accessory 

 glands undergo between this time and the ecdysis are 

 confined to increase in size. The development of the 

 penis commences during the ecdysis ; it grows out of 

 the cell-mass placed above the external sexual organs, 

 and is a globular body divided by a dorsal furrow. 

 Even during the ecdysis abundant production of sperm- 

 cells takes place ; these push into the vasa deferentia 

 and widen them until they are sack-like. The 

 epithelium flattens, and finally appears as a scarcely 

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