The life history of Diplodiscus temporatus Staffokd. 645 



at some distance from the canal in an apparently solid mass of 

 tissue. Before the flame cells have become completely differentiated, 

 however, they are put in communication with the canal through a 

 capillary tube. The lumen of this capillary becomes apparent first 

 near the flame cells, and only later acquires its connection with 

 that of the water vascular trunk. 



The reproductive system. 



The first indication of the reproductive system is seen after 

 the primordia of the digestive and Avater vascular systems have 

 been differentiated. A dense mass of cells becomes localized in the 

 median plane of the embryo between the posterior ends of the caeca 

 and the excretory bladder. At first there is no distinction betAveen 

 the parts of this mass which are to give rise to the male and to 

 the female reproductive organs. In the later development of the 

 embryo, this primordium becomes differentiated into a mass of cells 

 which represent the ovary, a mass from which are developed the 

 testes, and a ventrally situated mass which gives rise to the penis 

 with its sheath. These larger masses are connected by strands of 

 cells from which the male and female ducts are developed. In 

 general my observations confirm those of Schwarze, except in the 

 matter of the first appearence of the primordium. 



The nervous system. 



The first differentation of nervous tissue takes place in the 

 region of the future brain. The cytoplasm in a sharply defined 

 area above the primordium of the oesophagus becomes filled with 

 very fine fibres among which there may be distinguished a few 

 scattered nuclei. These nuclei differ very markedly in appearance 

 from those of the surrounding meristem cells. The limits of the 

 nervous tissue becomes marked out by the arrangement of the paren- 

 chyma nuclei about its periphery to form the rudimentary sheath. 

 The two bilateral masses of nervous tissue — the lobes of the brain — 

 become connected together by a strand which arises through the 

 fusion of two outgrowths, one from either mass. The main branches 

 of the nervous system arise as anterior and posterior outgrowths 

 from the brain. In none of my material have I been able to recog- 

 nise the pigmented eye spots which have been described for Amiihi- 

 stomum suhdavatum by Looss (1892). 



