84 



TISSUE RESPIRATION IN INVERTEBRATES 



other species the respiratory rate of the midgut 

 gland is higher in the male while that of the gill 

 is higher in the female (Vernberg, 1956; Belding, 

 Field, Weymouth, and Allen, 1942). 



Among insects, the cockroach {Periplaneta 

 americana) exhibits a certain consistency as 

 regards sex differences in the respiratory rate 

 of its various tissues. With the exception of the 

 foregut, all tissues in the male cockroach re- 

 spire at a higher rate than do those in the female 

 (Barron and Tahmisian, 1948; Allen and Rich- 



ards, 1954; Perez-Gonzalez and Edwards; 1954; 

 Sacktorand Thomas, 1955; Kubista, 1956; Young, 

 1958). In several other species of insects, how- 

 ever, tissues of the female have a higher respir- 

 atory rate than have those of the male (Graham, 

 1946; Allen and Richards, 1954), Furthermore, 

 Samuels (1956) found that the endogenous respir- 

 ation of teased thoracic muscle is approximately 

 equal in both sexes of the Madeira cockroach 

 {Leucophaea maderae) . 



VARIATION IN RESPIRATORY RATE WITH AGE 



Studies on the variation in endogeneous respir- 

 atory rate with age have been carried out on three 

 species of pelecypod mollusks, namely, the oys- 

 ters Crassostrea virginica (Hopkins, 1930) and 

 Gryphaea angulata (Chapheau, 1932), and the qua- 

 hog Mercenaria mercenaria (Hopkins, 1930, 1946). 

 In each of these species the respiratory rate was 

 found generally to decline with advancing age. 



What effect aging may have on the respiratory 

 rate of arthropods is not easy to evaluate. The 

 level of respiratory metabolism in crustaceans 

 and insects depends so completely upon the stage 

 of an animal in the molt cycle or life cycle that 

 its relation to the animal's chronological age is 

 often obscure. 



VARIATION IN RESPIRATORY RATE DURING 

 CRUSTACEAN MOLT CYCLE 



Increase in size in arthropods is discontinuous 

 and periodic. It occurs only at the time of ecdy- 

 sis when the old exoskeleton is cast off, to ex- 

 pose the new soft one underneath. Through uptake 

 of water, as in some crustaceans, or uptake of 

 air, as in some crustaceans and insects, the 

 soft new exoskeleton is rapidly enlarged to 

 greater dimensions before it becomes hardened 

 by tanning and, in the case of crustaceans, cal- 

 cification. Growth (i.e., increase in the amount 

 of body tissue), although a more extended proc- 

 ess than is increase in size, nevertheless is 

 timed to coincide with other preparations for 

 ecdysis and with subsequent post-ecdysial 

 events. 



Two studies involving the respiration of crusta- 

 cean tissues during the molt cycle are cited in 

 Section 2. In the first (Krishnan, 1954), the 

 cyanide-insensitive respiration (with added 

 fructose) of muscle from the green crab (Car- 

 cinus maenas) proved to be lowest during the 

 period just preceding ecdysis; the rate of respir- 

 ation rose during the soft-shelled stage immedi- 

 ately following ecdysis and reached a maximum 



during the intermolt period. In a second study. 

 Skinner (MS) traced changes in endogenous 

 respiration shown by integumentary tissues of 

 the land crab (Gecarcinus lateralis) . Oxygen up- 

 take is highest during the period just preceding 

 ecdysis, being 1.6 times that recorded during 

 the intermolt period. The apparent contradiction 

 between these two sets of results can be ex- 

 plained as follows: metabolism of muscle can be 

 expected to be maximal during the non-growth, 

 intermolt stage when the animal is active, while 

 the metabolism of integumentary tissues pre- 

 sumably will be highest during the premolt 

 period when these tissues are synthesizing the 

 new exoskeleton. 



To induce pre-ecdysial changes, ecdysis, and 

 (if the animal survives) post-ecdysial altera- 

 tions in a decapod crustacean, one need only 

 remove both eyestalks, for in these structures 

 are certain neurosecretory cells (X organ cells) 

 that synthesize and release a neurohormone 

 capable of inhibiting molting. Before its release, 

 the molt-inhibiting hormone is stored within the 

 eyestalks in the sinus glands, which consist of 



