NIDAMENTAL TISSUES 



479 



con 



from man. This section shows a compound alveolo-tubular gland with 

 a simple columnar secreting epithelium. The cells of this layer are clear 

 and secrete continu- ^ 



ously without a /^ ^v?/ 



degeneration and re- 

 newal of their cyto- 

 plasm. The secretion 

 is not plainly visible 

 at any stage of its 

 elaboration, and no 

 trophospongia have 

 been described. The 

 nucleus is round and 

 placed close to the 

 proximal end. Many 

 concretions are found 

 in the lumen of this 

 gland. 



Another form of 

 male-carrying fluid 

 is secreted by the sper- 

 matophoral glands of 

 certain crustaceans, as the lobster and the crayfish. This fluid is 

 secreted by the walls of the sperm ducts (Fig. 450), and it not only 

 serves as a vehicle to carry the mass of sperm out of the male organs, 

 but it also forms a semifluid covering around them and attaches 

 itself to a receiving plate on the female body and hardens, preserving 



the life of the spermatozoa for 

 months or even years until they are 

 needed to fertilize the eggs. When 

 this time comes, the female surface 

 secretes a fluid which softens the hard- 

 ened sperm fluid and brings the dor- 

 mant spermatozoa back to activity. 

 Such a package is known as a sper- 

 matotheca. 



Other carrying fluids for the sper- 

 matozoa are to be found in many 

 other animal forms. A step in the 

 organization of this apparatus may be 

 seen in the salamander, the male of 

 which secretes a covering for the sperm. This takes place in the 

 thickened folds of integument which border upon the cloacal open- 



sec 



FIG. 449. Part of several acini of the human prostate gland. 

 con., concretion; mus.f., smooth muscle fibers; bl., blood chan- 

 nel; sec., coagulated secretion. (After LEWIS, in " Stohr's 

 Text-book of Histology.") 



FIG. 450. Transection of the seminal 

 passage of a lobster, Homarus. Shows 

 the epithelium that secretes the heavy, 

 sticky, spermathecal covering for the 

 masses of spermatozoa. (After H. 

 HERRICK.) 



