TESTIS 339 



duce little waves in the substance in which they swim. But who would believe that in 

 these a human body was hidden? Yet we have seen such with our own eyes. For 

 while we were observing them attentively, a large one threw off its surrounding mem- 

 brane and appeared naked, showing distinctly two legs, thighs, breasts and arms. The 

 cast-off skin, drawn upward, covered the head like a cap, and it was a delightful and 

 incredible sight. Because of the minuteness of the object, the sex could 

 not be distinguished. After the little creature had lost its membrane it 

 soon died." 



This is a gross presentation of the preformation theory, according to 

 which the various parts of the adult are represented in the very young 

 embryo. It was held by many who could not verify such observations. 

 An alternative theory is tha.t of epigenesis, according to which the body FlG> 338 

 and its parts arise out of formless substance. Descartes (1664) wrote 

 that the source of a new individual "seems to be only a confused mixture of 

 liquors, which, serving to leaven one another, become heated; some of their agitated 

 particles dilate, and press upon the others, gradually disposing them in the way neces- 

 sary to form organs." Such physico-chemical speculations, however, are quite as 

 imaginative as any views of the preformationists and Descartes's epigenesis was early 

 characterized as " a very lame account of the forming of an animal." Nevertheless, 

 the doctrine of epigenesis, as advocated by Harvey (1651) and Wolff (1759), prevailed 

 over the cruder ideas of preformation. If, however, the spermatozoon can contribute 

 to the production of only one of the myriad forms of animals, even the sex of which is 

 apparently predetermined, it is evident that the spermatozoon must possess a very 

 definite chemical composition, and perhaps a corresponding ultra-microscopic structure. 

 Doubtless there is a preformation no less remarkable than that expressed through 

 the active imagination of Dalenpatius. 



Tubuli Recti and the Rete. The large convoluted tubules are 140 ft 

 in diameter. As they pass toward the epididymis they decrease in size; 

 they receive branches at acute angles and their windings diminish. 

 Sexual cells disappear, leaving only the sustentacular cells in the form of a 

 simple columnar epithelium. This flattens abruptly to form the lining of 

 the straight tubules. Both the straight tubules and the rete are lined 

 with a simple epithelium of low cells. In some places these are very flat, 

 suggesting endothelium; in others they are columnar., The characteristic 

 dilatations of the rete tubules are shown in Fig. 339. They contain 

 spermatozoa and immature sexual cells together .with pigment granules 

 and broken down cells. 



EPIDIDYMIS. 



The efferent ducts, which pass from the rete to the duct of the epididy- 

 mis, are lined with an epithelium in which groups of columnar cells alter- 

 nate with those which are cuboidal (Figs. 340 and 341). Thus the inner 

 surface of the epithelium has depressions suggesting glands, but the basal 

 surface is free from outpocketings. The epithelium is generally simple, 

 although in the tall parts it may appear two or three layered. The cells 

 contain fat, pigment, and other granules, and produce a secretion which 



