92 



TISSUE RESPIRATION IN INVERTEBRATES 



enzymes of primary importance in cellular 

 respiration. The members of the chain are 

 thought to be aligned as follows: 



succinate 



i 

 DPNH-^flavoproteins-^cytochrome b—* 



cytochrome c— »cytochrome a-^cytochrome oxidase 



hydroquinone (or) ascorbic acid (or) 

 /)-phenylenediamine. 



dart sac: Found in one superfamily of land 

 snails, the Helicacea; consists of a muscular 

 caecum arising from the vagina and contains 

 a fine-pointed calcareous shaft. The shaft is 

 exchanged by the hermaphroditic partners 

 during courtship and serves as a releaser 

 stimulus for courtship behavior. 



dehydrogenases: Enzymes that are generally 

 DPN- or TPN-linked and that catalyze the 

 oxidation of certain metabolites. Neither 

 DPN nor TPN, however, is required by suc- 

 cinic dehydrogenase, which transfers elec- 

 trons to the cytochrome chain directly. 



dialysis: A method for the separation of large 

 molecules from small by means of their un- 

 equal rates of diffusion through natural or 

 sjmthetic membranes. 



diapause: The condition of arrested growth, de- 

 velopment, or reproductive activity that occurs 

 at a given stage in the life cycle of many arth- 

 ropods, notably certain hemimetabolous and 

 holometabolous insects. 



differential manometer: See Barer oft, Fenn, 

 and Thunberg respirometers. 



digestive diverticula: See midgut gland. 



2, 4-dinitrophenol (DNP): Dissociates or un- 

 couples ATP synthesis from aerobic respira- 

 tion. 



diphosphopyridine nucleotide (DPN): Or coen- 

 zyme I; a hydrogen acceptor that is reduced 

 by a variety of substrates in the presence of 

 specific dehydrogenases; in turn, it reduces 

 a flavoprotein. 



ecdysls: In arthropods, the act of shedding or 

 casting the exoskeleton (shell). 



electron transport system: See cytochrome 

 system. 



endogenous respiration: Respiration without 

 added substrate. 



endoplasmic reticulum: An intracellular cj^o- 

 plasmic system consisting of tubules and 

 vesicles that form a continuous network of 



membrane-bound cavities; some of the mem- 

 branes have small granules (ribonucleopro- 

 tein particles) attached to them, so that these 

 membranes may appear rough-surfaced. 



ethylenediaminetetraacetlc acid (EDTA): Or 

 versene; a complexing agent used to chelate 

 divalent metals and so effectively remove 

 them from solution. 



extinction coefficient: See absorbancy. 



eyestalk extract: The supernatant obtained when 

 eyestalks of a decapod crustacean are homog- 

 enized, boiled, and centrifuged. 



fat body: In insects, a tissue that fills the body 

 cavity and contains large amounts of fat, pro- 

 tein, and glycogen. 



femur: The third (counting distad) and often the 

 broadest segment of the leg of an insect. In 

 the metathoracic leg, the femur may be con- 

 siderably enlarged to contain the muscles 

 used in jumping (as in a grasshopper or 

 cricket) . 



Fenn respirometer: A type of differential 

 respirometer; consists of two vessels con- 

 nected by a horizontal capillary tube contain- 

 ing an oil drop. As volume or pressure changes 

 within the respiration chamber, the oil drop 

 moves. 



flavoproteins: A group of conjugated proteins 

 of primary importance in the electron trans- 

 port system. 



fluorescence: The light emitted by a molecule 

 as a result of absorption of radiation from an 

 external source; persists only during irradia- 

 tion; is of longer wave length than is the in- 

 cident light. 



giant axon: A t3^e of nerve fiber of exception- 

 ally large diameter; found in lower verte- 

 brates and in certain invertebrates, including 

 annelids, crustaceans, insects, and cephalopod 

 mollusks; permits rapid conduction of nerve 

 impulses. 



gizzard: In Aplysia and other Aplysiomorpha 

 (opisthobranchiate mollusks) , most of which 

 feed by cropping live seaweeds with paired 

 jaws and radula. The gizzard has two cham- 

 bers, an anterior one for masticating and a 

 posterior one with delicate teeth for straining. 



hemimetabolous: Refers to an insect that under- 

 goes incomplete metamorphosis (egg — ♦ 

 nymph — »adult) . 



hepatopancreas: See midgut gland. 



holometabolous: Refers to an insect that under- 



