Pomona College, Claremont, California 69 



motor and probably some sensory fibers in these. Sense cells and 

 an epithelial plexus were not clearly seen in this form. Retzius 

 found sense cells in the skin chiefly about the mouth opening, in 

 the tentacles and the tube feet. In this form the peripheral nerve 

 fibers were not found. Crozier, 1915, discusses the sensory reac- 

 tions of Holothuria surinamensis Ludwig. 



The nervous system does not have to be intact for the act of 

 autotomy but it is more successfully carried out when it is unin- 

 jured. 



The animals are reactive to tactile, vibratile, photic, and chem- 

 ical stimuli, and practically indifl'erent to heat in the way of a 

 sensation. 



The parts of the body are sensitive in the following order, 

 beginning with the most sensitive : (1) tentacles, (2) anterior end, 

 (3) posterior end, (4) papillae, (5) pedicels (Podia), (6) mid- 

 body surface. 



The tube-feet discs are positively stereotropic. This shows in 

 the righting reaction. The arms are photokinetic, negatively pho- 

 totropic ; they do not respond to increase in light intensity, but re- 

 spond negatively to decrease in light intensity. The whole surface 

 is sensitive in this way. The fluorescent skin pigment is possibly 

 concerned. 



Dissolved substances representing those homologous to human 

 taste qualities for sour, bitter sweet, salt and alkaline, are effective 

 as stimuli. 



Crinoidea 



There are three distinct parts of the nervous system : 



1. The superficial epidermal. 



2. The deep oral system, according to the suggestions of 

 Delage and Herouard. 



3. The deep aboral system. 



The superficial oral system is much like the radial and circum- 

 oral system of starfish, with the nerve ring and radial nerves run- 

 ning down the surfaces of the ambulacra) grooves in each arm with 

 branches to the surface and to the little elevations covered with 

 sense hairs. 



The deep oral system according to Delage and Herouard's 

 interpretation is in the connective tissue under the epidermis and 

 consists of a central nerve ring and strands down each arm with 

 branches to the pinnacles. 



The deep aboral system develops later than the oral in the 

 young form. It is in the center of the so-called chambered organ. 

 There is a central mass of nervous matter in the chamber ; strands 

 run out from this towards the arms and fork but are united again, 



