PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 121 



other segmented animals, as well as in annelids, and also in the polyclad 

 larva (see Fig. 35, Z)) preceding posterior elongation, though segmentation 

 does not occur. It is apparently associated with posterior elongation of 

 the body, whether by formation of segments or not. In early stages of 

 embryonic elongation of Tubifex tubifex, an oligochete, susceptibility 

 shows only the posterior arm, that is, it decreases from the posterior seg- 

 ment-forming region anteriorly without evidence of higher susceptibility 

 in the head region (Fig. 38, A, B), according to Hyman (1916a). The ac- 

 tivity of the rapidly developing segments appears to dominate the whole 

 embryo. Somewhat later, however, when segments between the head and 

 the posterior growing region have undergone further development, the 

 U-shaped gradient characteristic of later, and probably also of earlier, 

 stages appears (Fig. 38, C). 



A B 



Fig. 38, A-C. — Differential susceptibility of embryonic stages of Tubifex tubifex. A, B, 

 earlier, and C, later, stages (from Hyman, 1916a). 



Respiration in relation to body-level has been determined in several 

 annelid species, both polychetes and oligochetes. Considering the data 

 with some departures from order of appearance, Hyman and Galigher 

 (192 1), using the Winkler method, found a U-shaped gradient of oxygen 

 uptake, with the posterior end usually higher than the anterior, in Nereis 

 virens, N. vexillosa, and Lumbriculus inconstans. Shearer (1924), using the 

 Haldane respirometer, found the oxygen uptake of anterior pieces of an 

 earthworm (species not given) at least twice as high as that of posterior 

 pieces and a similar difference in the oxygen uptake of acetone powders of 

 similar pieces. Since he used only anterior and posterior pieces, his data 

 do not show whether a U-shaped gradient was present in the species used. 

 In a later paper (Shearer, 1930) he concludes that his earlier data were in- 

 correct but presents no new determinations on the earthworm. Perkins 

 (1929) found a slight U-shaped gradient of oxygen uptake in earthworms 

 {Lumhrlcus sp.; Allolobophora sp.) but noted that it did not correspond 

 with the gradients of total iodine equivalence, extractable sulphydryl, and 





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