The Effect of Some Anions and Cations Upon the Fluxes and Net Uptake of Chloride in the Larva of Aedes Aegypti(L.), and the Nature of the Uptake Mechanisms for Sodium and Chloride

1. The anal papillae of the aquatic larva of Aëdes aegypti are responsible for 90% of the steady-state exchange of chloride. 2. The relationships between chloride flux and external chloride concentration are approximately described by the Michaelis equation. 3. There is net uptake of chloride, independent of uptake of sodium, from KCl, CaCl2 and NH4Cl, probably in exchange for OH' or HCO'3, but the rate is much slower than from NaCl. The following ions stimulate influx of chloride from 0.1 mM/l. KCl: H+ = Na+ < K+ The following ions inhibit it: OH' > HCO'3 > NO'3. 4. Movements of sodium and chloride ions are explicable in terms of an anionic and a cationic carrier located in an osmotic barrier in the papillae, the carriers being functionally coupled to sodium and chloride pumps located at the inner surface of the barrier. 5. An attempt is made to relate these findings to recent electron microscopical studies of the papillae.

The Permeability and Structure of the Cuticle of the Aquatic Larva of Sialis Lutaria

1. The permeability to water of the cuticle of Sialis larvae has been measured, using heavy water as tracer. The penetration was slow, the permeability constant being only 1.8 x 10-2 cm./hr. at 20° C. There was no obvious difference between the rate of water influx and outflux. The rate at which water penetrated into the tissues from the blood was much greater than through the cuticle. The Q10 for diffusion through the body surface was high, lying between 3.0 and 3.8. The osmotic uptake of water was calculated to be about 1% of the body weight per day at 10° C. 2. Drinking of water did not occur in normal larvae, but in larvae with the blood volume reduced, osmotic uptake of water through the gut did take place and the gut wall was much more permeable to water than the cuticle. A similar intake of water probably occurred during moulting. 3. The permeability of the cuticle to chloride was measured and also found to be of a low order (P = 1.04 x 10-4 cm./hr. at 17° C.). Sodium diffused out of the larva at the same rate as the chloride. 4. Histological examination of the cuticle showed that in the abdomen it was thin and consisted of a 7µ. thick endocuticle and a 1 µ epicuticle. Over the thorax it was thicker, and a polyphenol layer was present as the outer layer of the epicuticle. There was indirect evidence of the presence of a wax layer. 5. Wax was extracted from the cuticle, and the thickness of the layer from which it was derived was estimated by means of a monolayer technique. In the cuticle of the abdomen and gills the thickness averaged 0.1 µ. 6. The permeability to water of the cuticle was compared with that of terrestrial insects and was found to be much greater. This difference was not due to the thickness of the wax layer but probably to some physical properties of the wax. The cuticle of Sialis larvae showed no ‘critical temperature’ or sudden change in the permeability properties with temperature over the range of temperatures studied.

Ionic Regulation and Water Balance in the Aquatic Larva of Sialis Lutaria

1. The electrolyte composition of the blood, tissues and excretory fluid of the aquatic larvae of Sialis lutaria has been measured, and the regulation of the concentrations of sodium, potassium and chloride in the blood studied in detail. 2. In the normal larvae these ions are not present in the excretory fluid. Potassium and, perhaps, sodium are reabsorbed in the rectum but chloride is never present in the rectum. 3. If these ions are present in the outside medium they are taken into the larvae through the gut. The blood concentration is regulated by the excretion of these ions via the rectal fluid. Potassium is rapidly excreted but chloride tends to be retained in the blood. Sodium is removed more rapidly than chloride. 4. Water enters the larvae by osmosis through the cuticle, but can also be absorbed through the gut by osmosis or together with sodium ions. The water intake is balanced by excretion of rectal fluid. The factors affecting the rate of water excretion have been studied. 5. The larvae are unable to survive in hypertonic saline solutions. This is due to their inability to make good osmotic water loss or to produce a hypertonic excretory fluid.

The Excretion and Storage of Ammonia by the Aquatic Larva of Sialis Lutaria (Neuroptera)

1. A study has been made of the excretion and storage of ammonia by the aquatic larva of Sialis lutaria. 2. About 90% of the nitrogen excreted by the larva of Sialis during starvation was in the form of ammonia. The daily ammonia output averaged 10 µg. N/100 mg. wet weight. 3. Ammonia was found to be excreted into the hindgut, presumably via the Malpighian tubules. The concentration of ammonia in the hindgut fluid averaged 136 mg. N/100 ml. 4. Evidence was obtained that the tissue fluids are not maintained completely ammonia-free. Thus the total ammonia content of the body averaged 1.0 µg. N/100 mg. wet weight of tissue. The concentration of ammonia in the haemolymph averaged 0.50 mg. N/100 ml. 5. Evidence was obtained that the larval tissues are capable of ‘storing’ appreciable quantities of ammonia. Thus ammonia did not accumulate in the tissue fluids of larvae prevented from excreting for a period of days. Furthermore, it was found experimentally possible to raise the concentration of ammonia in the tissue fluids, the ammonia subsequently disappearing. The possible significance of this ‘storage’ mechanism was discussed. 6. The method used for raising the concentration of ammonia in the tissue fluids, by immersing the larva for some time in a solution of dilute ammonia, was considered in some detail, particularly with respect to toxic effects. When the concentration of ammonia in the haemolymph had reached a level in the region of 7.0 mg. N/100 ml. toxic symptoms started to appear.

XII. On the apparent relation of the nerves to the muscular structures in the aquatic larva of Tipula crystallina of de geer

To avoid as much as possible errors that might be attributable to a faulty mode of examination, the figures and photographs have all been made from the larvæ alive, and in their natural medium, except two instances in the drawings and one in the photographs. After alluding to the effects of various reagents which were generally found useless in “differentiating” the fine nervous structures, and the ordinary mode of branching in the nerves from the ganglionic chain, two particular methods of termination are selected as illustrative of the relation between the muscular and nervous tissues. One, termed the “flabelliform,’’ where the nerve on approaching the muscular sheath expands into a fan shape, and with its fine granular and nucleated contents embraces the muscle in form of the letter A, without any evidence of the granulai matter and sarcous elements being in absolute contact; the other, called the “stapiform” or stirrup-shaped. The latter, in its early stage, is knobbed in appearance. This, the early stage, is shown gra­dually passing into the cellular, looped, or stirrup form, embracing the fine muscular structure somewhat obliquely, or passing entirely round it, and projecting beyond its edge. In this form also there was no evidence of any union of the granular contents with the sarcous elements, though firm union existed between their sheaths or outer membranes. Fine networks, ending apparently in a granular irregular spot with a pale centre and uniting, are pointed out. The relation and union of short muscles passing between others, and nerve-fibres lying along­ side them, with flabelliform expansions, are remarked on, and shown in the figures and photographs. Muscles undergoing degeneration, or the metamorphic change, are noticed, and in no instance could a nerve-fibre be seen attached to them, or a fibre that could with certainty be traced to any nerve or ganglion. No change was observed of a definite character, as regards the mode of union, under muscular contraction. Some of the finest muscular fibres are passed by for special reasons, as constant motion &c. Attention is called to the blood-corpuscles, or to corpuscles which, for convenience, are called creeping corpuscles, and several figures given. The peculiarities of these bodies are regarded as of consi­derable importance, and, coupled with a remark in Dr. Beale’s contri­bution to the Transactions of the Royal Society, read May 21st, 1863, in reference to the movement of all forms of living matter.