PLANARIAN WORMS. 



101 



body (Fig. 65, /), from which nerves pass in different 

 directions, but a true nerve-cord is not known with cer- 

 tainty to exist.* The eyes are very simple, indicated by 

 two or more, sometimes 

 thirty, dark pigment spots. 

 In certain forms, such as 

 Macrostomum, there is a ru- 

 dimentary ear (otocyst). 



Most of the Planarians, 

 land and aquatic, have organs 

 of defence in the form of 

 minute, stiff rods, either 

 coiled up in an irregularly 

 spiral manner, or short and 

 straight, contained in oval 

 cells. These bodies are shot 

 out in great numbers when 

 the animals are irritated, but 

 are not retractile, being pro- 

 jected clear from the skin. 

 In being neither retractile 

 nor barbed, they differ from 

 the lasso-cells of the jelly- 

 fishes. That, however, they 

 are true urticating organs 

 has been proved by Mr. 

 Thwaites (at the suggestion 

 of Mr. Moseley), who, on 



f nn rli i n rr opvfoin fWlnnpsp t, male genital-canal ; k, oviducts; I, 



touching ceitain ueyionese gperm . sa( ?. m ^ opening into the oviduct, 

 land - planarians with his -AfterQuatrefages. 

 tongue, felt an unpleasant tingling or scalding sensation, 

 accompanied by a slight swelling. 



* Sclimarda describes the nervous system of Bipalium dendrophiluz 

 as formed of two pairs of ganglia, from the hinder of which arise two par- 

 allel nerve-threads, which dilate into at least nine swellings. Moseley 

 discovered no more than one pair of ganglia in the species of Bipalium 

 he examined. Blanchard has demonstrated ""successive ganglionic 

 repetitions along the nervous-threads at the right and left sides of the 

 mid-line of the body of a large Planarian (Potycladus Gayi Blanch.). " 

 Clark's " Mind in Nature," p. 253. 



