Meyen's Report for 1839 on Physiological Botany. 2G9 



development. Pagurus, Galathaa, and Hyas come out in a 

 less developed state, since at the time of quitting the egg they 

 do not even possess a trace of legs or branchiae. Astacus ma- 

 rinus, on the contrary, and Astacus fluviatilis are at that 

 time already provided with all the legs and branchiae belong- 

 ing to their organization. Other parts with* which all Deca- 

 pods appear to be then already furnished are in some at that 

 time only slightly, in others, on the contrary, exceedingly far 

 developed with respect to size. This relates especially to the 

 antennae. On the other hand, some possess in the com- 

 mencement parts w T hich are subsequently entirely lost ; as, 

 for instance, in Astacus marinus appendages on the legs for 

 swimming, and in Hyas Araneus a considerably long spine 

 on the upper side of its dorsal shield, while in other Decapods 

 such parts never occur. Or, in some, parts vanish, which in 

 others are permanent, as the snout in the Paguri, and the 

 lateral laminae of the fan in Hyas ; and other parts again 

 undergo such considerable changes in their form, that it 

 becomes quite different, as, for instance, central lamina 

 of the fan, the foot-jaws, and the antennae of several spe- 

 cies. One of the most remarkable phaenomena is, however, 

 this ; — that in Decapods which inhabit the sea the members 

 they employ for locomotion are in the commencement so or- 

 ganized that they can solely or principally be used for swim- 

 ming (as appears to be the case with the Lobster) ; in the 

 freshwater Crab, on the other hand, when it leaves the egg 

 those apparatus have such a structure that they can only be 

 employed for walking. 



In conclusion, I would still direct attention to the circum- 

 stance, that although several Decapods, perhaps even the 

 greater number of them, have in the commencement with re- 

 spect to the form of their members great similarity with the 

 Schizopoda, and especially with species of Mysis, yet the de- 

 velopment of the two tribes of animals is very different in se- 

 veral other respects. 



XXXI. — Report of the Results of Researches in Physiological 

 Botany made in the year 1839. By F. J. Me yen, M.D., 

 Professor of Botany in the University of Berlin. 



[Continued from p. 144.] 

 From C. Sprengel, the writer on Rural QEconomy, we have re- 

 ceived a work on Manures*, which is not only of high prac- 



* Die Lehre vom Diinger, oder Beschreibung aller bei der Landwirthschaft 

 gebrauchlicher vegetabilischer, animalischer und mineralischer Dungerma- 

 terialien, tiebst Erklarung ihrer Wirkungsart, Leipzig, 1839, 8. 456 Seiten. 



