DR. THEODOR NEUMANN. 227 



The male individuals keep up their movability and use 

 it to find and fructify the females. 



3. The sexes are united in the same individual and 

 make a fructification of the eggs possible through the 

 same animal's sperma. 



4. This case is limited to parasites only : from the eggs 

 of sessile animals with separated sexuality larvae are de- 

 veloped which live free for some time, copulate in the free- 

 living state, and then become sessile again. In this case 

 the grown forms are females only, which bring the eggs 

 to maturity; for since the males have filled their purpose 

 of life by delivering their sperma to the females, they 

 perish soon after and do not enter the state of parasitism. 



Within these limits many peculiarities of individual 

 species are of course encountered. Bilharzia haematobia 

 (Distomum haematobium) is a very dangerous parasite 

 of man, especially in Egypt and in Abyssinia. It lives 

 in the veins, especially in the portal vein, but descends 

 to the vessels of the abdomen for the purpose of deposit- 

 ing its eggs, which sometimes block the circulation, 

 through their enormous number. True, they cannot get 

 out from here at once, as the blood system is closed all 

 round ; through the irritation, however, which they exert 

 on the walls of the blood vessels, sores spring up which 

 break through into the urethra and the rectum and thus 

 allow the eggs to escajje. The blood also flows into these 

 canals, and we have before us a rase of that dangerous 

 disease called h?pmaturia, when blood instead of urine is 

 discharged. Bilharzia has separate sexes. We under- 

 stand that the constant presence of two animals made 

 hermaphroditis unnecns^ary. With this differentiation 

 into sexes we find also u change in the form of the body: 

 the male becomes rather broad, flat, and forms a canal 

 by bending over the rims of its body so that the slender, 

 round female may be received into it and carried around 

 for life. 



165 



