744 GEOLOGICAL SURVEY OF THE TEREITORIES. 



6. When fresh-water articulates pass by a very slow transition from 

 fresh into salt water, and when, during this transition, reproduction has 

 taken place, the new generation resists much longer the action of salt- 

 water than the ordinary individuals of the species. 



MARINE CRUSTACEA. 



7. The most common Crustacea of our shores die in fresh water, after 

 a time, varying with each species, but not passing beyond nine hours. 



8. Marine Crustacea plunged in fresh water lose the salts (especially 

 the chloride of sodium) with which their tissues are impregnated. 



9. In the greater number of cases the presence of chloride of sodium 

 is a part of the indispensable conditions of the existence of marine Crus- 

 tacea. This salt seems to be the sole necessity. 



10. Small individuals, and those which, having just moulted, have the 

 teguments thin, resist less tha,u the others the influence of liquids of 

 exceptionable composition. 



11. The difference between the densities of sea and fresh water can- 

 not be considered as the cause of the death of marine Crustacea in fresh 

 water. 



12. (Applicable to the two groups.) The principle of endosmose ex- 

 plains the absorption of salt by the thin tegument or branchial surfaces 

 of fresh-water articulates placed in sea-water; the diffusion of gases 

 and dialysis, operating with more energy for the chlorides of sodium 

 and magnesium than for the sulphate of magnesium, showing in virtue of 

 which cause that the chlorides alone of sea-water are absorbed. Finally, 

 dialysis explains how marine Crustacea, when placed in fresh water, 

 lose in this liquid the salts with which they were impregnated. 



So much has been said about the absence of life in the Great Salt 

 Lake, that an erroneous impression may prevail as to the life of that, 

 and similar though smaller lakes. With a view of imparting what 

 knowledge we now have as to this subject, in order to earnestly call the 

 attention of those^who live near the shores of Great Salt Lake., and 

 travelers and collectors to this subject, I will give a brief account of 

 what is known regarding articulate life in these saline waters. 



In 1852 Mr. T. E. Peale prepared for Stansbury's "Eeport on the 

 Valley of the Great Salt Lake of Utah," p. 379, an account of the insect- 

 life of the lake. He states that in a mass of exuviai of insects brought 

 from the shores of the Great Salt Lake, there was an abundance of the 

 larvae and exuvias of the pupre of Chironomus, and fragments of other 

 tipulidiTe. 



Afterward Mr. S. A. Briggs, of Chicago, noticed and figured in 

 '' Science Gossip," (Loudon,) a creature whose zoological position he 

 did not know. It was the larva of a species of Ephydra. 



This pupse-case was afterward described by me under the name Ephydra 

 gracilis.* The specimens were collected by Mr. Sereno Watson. Other 

 specimens of the lar^se, as well as pupae and adult flies, were collected 

 by Mr. S. A. Garman, and also by Mr. J. A. Allen, and are in the Museum 

 of Comparative Zoology at Cambridge, and will be described hereafter, 

 The Ephydra sometimes occurs in large quantittes. 



I have also received from Mr. Garman two si^ecimens of Gorlxa taken 

 by him from the lake. 



Undoubtedly other insects will be found in Salt Lake, and we trust 

 some one of the readers of this article will make a careful examination 



* American Journal of Science and Arts, Febuaryj 1871. 



