PLANARIAN WORMS. 101 
body (Fig. 65, f), 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 9, nccnca ete mage, aponth § 
6, buccal cavity ; ¢, esophageal orifice ; @, 
stomach ; ¢, branches of the stomach ; 
of Mr. Moseley), who, on ganglia ; "g, testes ; 2, vesicule Sona : 
7 d a, male genital-canal; %, oviducts; J, 
touching certain Cey. lonese sperm-sac 5 m, opening into the oviduct. 
land-planarians with his —After Quatrefages. 
tongue, felt an unpleasant tingling or scalding sensation, 
accompanied by a slight swelling. 
* Schmarda describes the nervous system of Bipalium dendrophilus: 
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 (Polycladus Gayi Blanch.).’’— 
Clark's ‘‘ Mind in Nature,’’ p. 258. 
