. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 488 BRYN M. JONES AND RONALD S. WILSON TABLE I Relationships between the depressant action of phenylthiourea on the rate of oxygen consumption at the beginning of spinning and the types of structures spun. For details see text. Os/gm. pupal \vt. hr. Mg. of agent Serial injected 24 hr. Types of cocoon spun no. previous to spinning Uptake at the beginning of Uptake at the end of spinning Range spinning P 6 nil 740 210 520 Normal P 8 700 260 440 Two- layered and closed P 1 700 280 420 Two-layered and closed P4
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 488 BRYN M. JONES AND RONALD S. WILSON TABLE I Relationships between the depressant action of phenylthiourea on the rate of oxygen consumption at the beginning of spinning and the types of structures spun. For details see text. Os/gm. pupal \vt. hr. Mg. of agent Serial injected 24 hr. Types of cocoon spun no. previous to spinning Uptake at the beginning of Uptake at the end of spinning Range spinning P 6 nil 740 210 520 Normal P 8 700 260 440 Two- layered and closed P 1 700 280 420 Two-layered and closed P4 520 280 240 Two-layered and open P9 500 250 250 Hammock-shape P 7 525 265 260 One-layered and open L 2 490 290 200 Hammock-shape P 2 385 210 175 Hammock-shape An important symptom of metamorphosis in Cynthia, as already described, is the striking fall in the rate of oxygen consumption, which begins two and a half days before the onset of spinning. The injection of phenylthiourea into silkworms during this pre-spinning period would be expected therefore further to depress the already decreasing rate of oxygen consumption. It is also reasonable to assume that this fall in the rate of respiration reflects the progress in the series of events of metamorphosis which is triggered off by the "pupation" hormone (Williams, 1947). The timing of the onset of spinning is therefore already under hormonal control, and the insertion of phenylthiourea into the blood just prior to the spinning period is unlikely to influence it. Accordingly, the compound was injected in solution into Cyntliia about 24 hours before spinning was due to begin. This stage was conveniently marked by. FIGURE 4. Series of structurally different cocoons spun by Cynthia after being injected 24 hours previously with varying amounts of phenylthiourea. From left to right in the photo- graph relative amounts of the inhibitor used were, nil, mg., mg., ing., mg., mg., and
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