DISCUSSION 



83 



recently been shown by Harvey (1961), who found 

 that carbon monoxide can stimulate oxygen up- 

 take (see also Kurland and Schneiderman, 1959) 

 and that 5 per cent of the total gas consumed may 

 be carbon monoxide. 



On the basis of their findings, these several 

 workers have concluded that during pupal dia- 

 pause in Cecropia (and also in three closely 

 related species of saturniid moths) cytochrome 

 oxidase does serve as the terminal oxidase. 

 They account for the fact that respiration of 

 diapausing pupae at reasonable oxygen tensions 

 and when unstimulated by dinitrophenol or by 

 injury is apparently carbon monoxide-, azide- 

 and cyanide-insensitive by pointing to the excess 

 of cytochrome oxidase in most tissues of dia- 



pausing pupae compared to the low concentra- 

 tions of cytochrome c (Shappirio and Williams, 

 1957a, 1957b). Thus, although a large portion of 

 the oxidase may be inhibited by a respiratory 

 poison, enough oxidase remains unbound to per- 

 mit the transfer of electrons from cytochrome 

 c to molecular oxygen. Clearly the apparent 

 insensitivity of diapausing pupal respiration to 

 the inhibitors of cytochrome oxidase is not an 

 actual insensitivity. Provided that respiration 

 is stimulated or, alternatively, provided that the 

 oxygen tension is lowered sufficiently for the 

 concentration of uninhibited cytochrome oxidase 

 to become rate-limiting, a sensitivity to carbon 

 monoxide, azide, and cyanide during pupal dia- 

 pause can be demonstrated. 



COMPARISON OF RESPIRATORY RATES 

 OF VARIOUS TISSUES 



\^ 



Let us leave the subject of respiratory en- 

 zymes and their inhibitors at this point and dis- 

 cuss certain other aspects of invertebrate tissue 

 respiration that have been investigated in the 

 papers cited in this volume. Among the most in- 

 teresting work is that which concerns the com- 

 parative respiratory rates of different tissues. 

 In three investigations (Shapiro, 1937, on Lim- 

 ulus Polyphemus ] Kerkut and Lave rack, 1957, on 

 Helix pomatia; Ghiretti-Magaldi, Giuditta, and 

 Ghiretti, 1958, on Octopus vulgaris) ganglionic 

 tissue proved to have the greatest endogenous 

 respiratory activity. In general, ganglionic tis- 

 sue respires most rapidly, foot or leg muscle 

 most slowly, and various other tissues at inter- 

 mediate rates (Chapheau, 1932; Shapiro, 1937; 

 Hopkins, 1946; Kawai, 1957; Kerkut and Laverack, 

 1957; Ghiretti-Magaldi, Giuditta, and Ghiretti, 

 1958; Higashi and Kawai, 1959; Kawai, 1959). 

 Among insects, flight muscles have consistently 

 higher endogenous respiratory rates than have 

 leg muscles (Perez-Gonzalez and Edwards, 

 1954). In most brachyuran crustaceans the mid- 



gut gland has a higher endogeneous metabolic 

 rate than has the gill. However, in certain active 

 terrestrial and intertidal species, the gill ex- 

 hibits a greater respiratory activity (Kermack, 

 Lees, and Wood, 1954; Vernberg, 1956). 



A comment concerning the particulate frac- 

 tions assayed by Ghiretti-Magaldi, Giuditta, and 

 Ghiretti (1957) is advisable. In order to facilitate 

 homogenization, these investigators chose to 

 freeze the tough muscles from the mantle and 

 tentacles of Octoptis vulgaris before fractionat- 

 ing them. In later work on Octopus (Ghiretti- 

 Magaldi, Giuditta, and Ghiretti, 1958), they again 

 used frozen muscle tissue for their preparations. 

 In still later studies on Aplysia, the sea hare 

 (Ghiretti, Ghiretti-Magaldi, and Tosi, 1959), 

 frozen buccal mass muscle, frozen midgut gland, 

 and frozen gizzard muscle were employed in the 

 preparation of slices and particles. Since freez- 

 ing disrupts both cells and intracellular organ- 

 elles of most tissues, the particulate material 

 used in these investigations may well have been 

 fragmented. 



SEX DIFFERENCES IN RESPIRATORY RATE 



The results of studies dealing in part with sex 

 differences in respiratory rate present no clear 

 picture. In some species of brachyuran crusta- 



ceans, the respiratory rate of both midgut gland 

 and gill is higher in the female than in the male; 

 in other species the reverse is true; in still 



