PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 119 



course, the total CO2 production of all organs at the different levels; and 

 the data on dye reduction in a related species, presented below, indicate 

 that gradients in dijfferent organs differ in direction. The ectodermal sus- 

 ceptibility gradient gives no information concerning internal organs. 

 However, the very slight variations in successive CO2 determinations on 

 the same lots 2, 4, and 6 hours after section indicate that they are phys- 

 iologically significant as indicating a definite respiratory pattern of the 

 whole. 



The gradient of the earlier larval stages of a Califomian Leptoplana is 

 apicobasal, like that of corresponding stages of Stylochus. Observations on 

 differential reduction of methylene blue in adults of this species and of a 

 planocerid closely resembling Stylochus appear to throw some further light 

 on the question of gradient pattern in these forms. When only the body 

 wall is stained, rate of dye reduction decreases from the posterior end ante- 

 riorly and from median to lateral regions. When animals are stained 

 throughout, internal reduction is most rapid in the cephalic ganglia and 

 decreases in all directions from them, more rapidly posteriorly than anteri- 

 orly. In both species susceptibihty of the ectoderm and body wall, like 

 dye reduction, shows a gradient decreasing from the posterior end anteri- 

 orly. Apparently, then, there are in these forms at least two gradients — • 

 an ectodermal and an internal — in opposite directions. It is a point of some 

 interest that the cephalic ganglia reduce more rapidly than other internal 

 organs. When the genital complex is present, it reduces more rapidly than 

 adjoining regions, but not as rapidly as the ganglia. The uncertainty as 

 regards interpretation of respiratory gradients of adult animals with dif- 

 ferent, more or less localized organ systems is well illustrated by these 

 polyclads. The different lines of evidence suggest that the primary gradi- 

 ent persists internally, apparently in relation to the nervous system, 

 while secondary gradient changes occur in ectoderm and body wall. In 

 cleavage and gastrula stages of the planocerid species rate of reduction of 

 methylene blue in low oxygen decreases basipetally from the apical region. 



ANNELIDS 



The bipolar migration of alkaline and acid substances in the egg of 

 Nereis at the time of polar-body formation and their accumulation, re- 

 spectively, in apical and basal regions indicate the existence of an axial 

 differential of some sort (Spek, 1930, 1934&). Spek suggests that the mi- 

 gration is due to an electrical factor, but the existence of such a factor im- 

 plies a physiological differential. 



