H. Rathke on the Metamorphosis of the Crusiucea. 263 
is doubtful to what genus it should be referred; most probably to 
my genus T’helmatophace. 
In Steudel’s Nomenclat. Bot. there is a plant Lemna punctata, 
Meyer, of which I am ignorant. 
Lemna obcordata, P. Beauv. and Vahl. as well as Lemna dimidiata, 
Rafin., are erroneously enumerated amongst the Lemnacee, since an 
inspection of authentic specimens from the authors themselves proves 
them to be species of ficcia. 
XXX.—Contributions to the History of the Development of 
the Decapod Crustacea. By Herrinricu RatTuKe*. 
One of the objects which I had proposed to myself for my 
tour through Scandinavia and Denmark, was an investigation 
of the Crustacea as regarded their development. Of Deca- 
pods which might serve as subjects for this investigation, se- 
veral, it is true, fell in my way; fewer, however, by far than 
I had expected: these were Astacus marinus, Pagurus Bern- 
hardus, Galathea rugosa, and a crab, which I consider to be 
Hyas Araneus. The details respecting these I design to make 
known, together with the results of the examination of various 
other animals, in a separate work; as, however, some time 
may elapse before its publication, I will here communicate the 
most essential particulars of what I have learned respecting the 
development of the above-mentioned Crustacea, in order, as 
soon as possible, to record.a testimony to the correctness of 
Thompson’s discovery, that even the Decapods, after they 
haye already quitted the egg, undergo a very considerable 
metamorphosis. 
1. Astacus marinus.— Embryos just on the point of hatch- 
ing, possess already five pairs of feet, and these are similar in 
form to those of the full-grown specimens. But to the coxz 
of each is attached a part representing a narrow and long ap- 
pendage of the leg, proceeding down it on its outer side, little 
inferior to it in length, and composed of two larger members, 
of which the inferior one again consists of ten smaller articu- 
lations, and carries a number of long bristles. The same also 
is the case with the foot-jaws (Kieferfussen) of the second and 
third pair, of which, moreover, the hindermost is even at this 
period the largest of all, and it is evident from this that the 
above appendix represents the subsequent palpus flagelliformis. 
The four posterior foot-jaws and the ambulatory legs have 
also in general a resemblance to the legs of the Schizopoda, 
especially to those of Mysis. But this similarity afterwards 
 *® From Wiegmann’s Archiv. (Part III. 1840.)—Translated and com- 
munieated by Mr. W. Francis. 
