257] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 63 



REPRODUCTIVE SYSTEM 



Only during a rather limited period in the year are the reproductive organs 

 to be found. Then they stand out definite and heavy, easily recognizable 

 among the other more transparent organs. The season of sexual maturity ex- 

 tends from about the first of November till the last of December, and during 

 this time a single individual will produce several eggs. The animals are her- 

 maphroditic but do not possess so complicated a series of organs as is generally 

 to be found in this class. In brief, the reproductive organs consist of paired 

 testes, a single ovary, with small vitelUne glands and atrium seminalis which 

 opens to the exterior by a short canal and pore situated on the ventral surface. 

 The organs lie close together just posterior to the pharynx rosette, ventral 

 to the intestine but to a greater or less degree displacing it. The group of 

 parts thus formed makes a noticeably clearer region, oval in shape, much larger 

 than the pharynx in extent and lying in the middle of the body. The two 

 testes are situated on the right and left of this transparent part with the ovary 

 between them and in all three instances the ducts open forward and ventrally 

 into the atrium. The vitelline glands, having their connection with the ovar- 

 ian duct, ramify for a short distance among the adjacent lobes of the intestine. 

 During the development of the egg, which takes place in the atrium, the other 

 organs become crowded to either side. 



The organs, themselves, are characteristic and vary little from the general 

 type. The testes are spherical with a rather large duct leading to the atrium. 

 This duct is very broad at the point where it leaves the testis and narrows 

 gradually toward the opening, which gives it a funnel-shaped appearance. 

 The wall of both testis and duct bears a layer of muscular fibers lying parallel 

 to each other. The wall is, however, of sufficient transparency to reveal the 

 mass of sperm cells lying within. Thruout the whole reproductive period, the 

 testes are tightly packed with sperm, all seemingly mature at least in size. 

 The ovary varies a good deal in size at different times during the sexual period. 

 It is made up of a mass of extremely large cells packed closely one above the 

 other, crowded into narrow plates, from six to ten completely filling this organ. 

 The shape is that of a pear but varies slightly toward the ovoidal. As the 

 eggs become mature at the lower end, they round out and draw away from 

 the mass Uttle by little until they escape into the duct leading to the atrium. 

 Fertilization probably takes place while the egg is still in the canal, which is 

 very short, or at the time it reaches the atrium. The immature eggs are 

 thin-walled with very large nuclei and finely granular protoplasm. By the 

 time the last egg has become mature, the ovary is very much diminished in 

 size and is ready almost to disappear. In the atrium, which by means of its 

 heavy wall becomes the egg-capsule, the ovum goes thru the maturation stages, 

 develops the yolk-cells, and gains the heavy wall so characteristic of it. The 

 atrium lies on the median fine and as the egg enlarges it becomes more and 

 more conspicuous. By the time the ovum is ready for laying, it has a size nearly 

 equal to that of the pharynx and has stretched the atrial wall to the limit, so 



