io6 PATTERNS AND PROBLEMS OF DEVELOPMENT 



Epiadis and Peachia show basipetal decrease in susceptibility and rate of 

 reduction in each tentacle and in the body. In colorimetric determinations 

 of CO2 production of distal and proximal pieces of the actinians Sagartia 

 luciae and Metridium marginatum no definite difference was found (Park- 

 er, 1929), but the data have httle or no significance.'^ 



Entodermal susceptibility and reduction gradients in these coelenter- 

 ates appear, in general, to be the same as the ectodermal. In well-fed 

 hydras and hydroids the entoderm of the apical region may cytolyze be- 

 fore the ectoderm; but in other regions entodermal susceptibility is ap- 

 parently about the same as that of the ectoderm, except locally in the re- 

 gion of recently ingested food undergoing digestion. In starved animals 

 entodermal susceptibility may be distinctly less than that of the ectoderm. 

 Entodermal dye reduction usually follows ectodermal reduction and pro- 

 gresses in the same direction. In the solid tentacles of hydroids and in the 

 Corymorpha stem with its core of supporting cells of entodermal origin it 

 can usually be seen that dye reduction is most rapid in the outer parts of 

 the entoderm cells, those parts next to the ectoderm. Respiration is prob- 

 ably very low in these cells, and dye reduction in them may be largely an 

 induced result of the much higher oxygen uptake of the ectoderm. The 

 question whether there is an intrinsic gradient in the entoderm of the 

 hydrozoa remains open. 



CTENOPHORES 



Differential susceptibility of Mnemiopsis, BoUnopsis, Pleurobrachia, 

 and Beroe decreases, in general, from the apical region in the oral direction 

 with increase in the oral region of Pleurobrachia and in the lobes of the lo- 

 bate forms, Mnemiopsis and Bolinopsis. The swimming-plate rows also ex- 

 hibit a very marked gradient in the same direction, but this may be altered 

 by differences in motor activity of the plates at different levels of a row. 

 In the higher, more rapidly lethal concentrations of various agents in 

 which movement of all plates is completely stopped within 1-2 hours, ces- 

 sation of movement and death of the plates and their bases with change 

 from the transparency of the living plates to opaque white begin at the 

 aboral (apical) end of the row and progress orally from plate to plate. In 



" The possibility of stimulation of the pieces following section or of laceration of the foot 

 in detaching the animals is not considered; time between section and determination is not 

 given; and only one set of determinations on each of four lots is presented. Moreover, since 

 the foot is a secretory organ, it may have a high CO, production, and this may be increased 

 by detachment, even without laceration. Determinations on at least three pieces— apical, 

 middle, and basal— must be made and repeated at different periods after section before any 

 conclusions can be drawn. See Child and Watanabe, 1933. 



