PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 117 



dividual is to be obtained not only from postembryonic stages of planari- 

 ans but from early embryonic stages of various animals and in the same 

 relation to gradient pattern. 



OTHER TURBELLARIA 



Observations on the zooid chains of the rhabdocoel Stenostomum, in 

 which morphological development of zooids precedes separation (Fig. 10), 

 show that rate of methylene blue reduction and susceptibility decrease 

 from the head region of each zooid after an early stage of zooid develop- 

 ment.^'' 



Susceptibility, as indicated by cytolysis, and the indophenol blue reac- 

 tion in eggs removed from the uteri, cleavage stages, and early larvae of 



A B C D 



Fig. 35, A~D. — Susceptibility gradients in eggs and developmental stages of Stylockiis 

 ijimai. A, egg removed from uterus; B, early larva; C, D, later larval stages. The indophenol 

 blue gradient is similar (after Watanabe and Child, 1933). 



the Japanese polyclad Stylochus ijimai show a gradient decreasing from 

 apical to basal pole (Fig. 35, A, B). In later larvae the apicobasal 

 gradient persists in the general ectoderm, but the cells of the two ciliated 

 bands also show a higher susceptibility and rate of indophenol reaction 

 than adjoining regions (Fig. 35, C), and in the most advanced larvae ex- 

 amined the whole posterior region shows increased susceptibility and rate 

 of indophenol reaction (Fig. 35, Z)). Conditions during metamorphosis are 

 not known. Determinations of CO2 production of pieces from different 

 body-levels of adults show a U-shaped gradient in most individuals (Fig. 

 36) . Whether the high CO2 production of the posterior region is associated 

 with the presence in it of the terminal genital complex is not certain. As 

 noted above, the posterior region shows increase in susceptibility and rate 

 of indophenol reaction in later larval stages, before there is any trace of the 



" Child, 1 9 246, susceptibility; t 934(7, dye reduction. 



