TRICLADIDA 



4 1 



apparently by the division and specialisation of scattered em- 

 bryonic cells in the parenchyma. The asexual reproduction of 

 Land Planarians is not fully proved, though it is known that 

 they repair injuries to the body completely, and that Bipalium 

 keivense is often found in hothouses, divided into fragments which 

 regenerate all the organs of the parent, but like the latter, do not 

 mature their sexual organs. 



Excretion. The excretory organs of Triclads consist of flame- 

 cells, canaliculi, and a pair of longitudinal canals, the external 



Cbr 



Fig. 18. Semi-diagrammatic view of the excretory system of Planaria lactea. (Partly 

 after Chickoff.) can, Capillary network on both dorsal and ventral surfaces ; gJbr % 

 branches of the intestine ; Ig, lateral branches of the digestive system ; In, longi- 

 tudinal nerve ; ph, pharynx, with intermuscular capillary excretory network arising 

 from the point marked pht ; tp, principal vessels of the excretory system, the 

 external opening of which is not certainly known ; vs, vesicula seminalis. 



openings of which, have not been satisfactorily ascertained. The 

 flame-cells are difficult to detect in Planaria lactea, and the latest 

 observer, Chickoff, 1 was unable to see them, although to him we 

 are indebted for figures of this system in P. lactea (Fig. 18) 

 and P. alpina (P. montana). In the latter, the flame-cells are 

 distinct, and may open directly into the two main canals or 

 indirectly through unbranched canaliculi. The pharynx possesses 

 a special supply of excretory tubules communicating with the 

 main canals. A similar system has been described and figured 

 in Gunda segmentata by Lang. 2 



1 Archives d. Biologic, torn. xii. 1892, p. 437. 

 - Mitth. Zool. Stat. Neapel, Bd. iii. 1882, p. 187. 



