Dr. Strahl on the Systematic Position of the Thalassine. 395 
escaping from the egg in the form of Zoéa—is not very difficult 
to answer; for the above-mentioned observers state particularly 
that the Zoée observed by them had something very peculiar 
about them, namely, the scale on the outer antenna. Philippi 
even figures this; and the peculiarity of the Paguride is 
that the thoracic legs are only subsequently developed, just 
like the appendages of the abdomen. In the subsequent deve- 
lopment, the legs appear no longer to occur with two rami; at 
least, Rathke says nothing decisive upon this point, although he 
particularly states, with regard to the maxillipeds, that these are 
biramose. 
Upon Galatea rugosa Rathke says but little. Its mature 
embryos agree in structure with those of Pagurus. But here 
our first question would be, whether these embryos have a scale 
on the outer antenna, this being absent in the perfectly deve- 
loped animal. From the materials available to us, which indeed 
are but scanty, it appears as if the mature embryos did not 
differ essentially from the fully developed animals in respect of 
the organization of the eyes and of the outer and inner antenne. 
That during development definite lower forms must be passed 
through does not appear to be the rule among the Crustacea. 
I am only acquainted with one instance which is in favour of it. 
Milne-Edwards states that he has observed that, in mature em- 
bryos of Naxia serpulifera, the first jot of the outer antenna 
is not anchylosed with the surrounding parts, but still exists 
separately (Annales des Sciences Nat. 2 sér. i. p. 331). From 
this we should expect to find something similar in the Palinuride 
and Scyllaride. But if the Phyllosomata be their larve, we 
must again hesitate, from what is stated above, before setting up 
Milne-Edwards’s observation as a rule. 
As above mentioned, the Thalassine and Astacine are not 
much compressed laterally, at least not in the same degree as 
many Palemones, and especially the Peneide; by this means it 
is of course possible that the sternum may become developed to 
a greater breadth. Many of the forms belonging here want the 
appendages of the first abdominal segment which act as externai 
male sexual organs. According to Thomson, the copulation of 
these also takes place in a peculiar manner. Perhaps, in con- 
nexion with this, the sternum of the female is constructed dif- 
ferently from that of the male. Not only are the sternal plates 
of the fourth thoracic segment considerably larger, as is likewise 
the case even in the male, but also those of the third segment, 
and consequently a peculiar way is established from the female 
sexual orifices towards the abdomen. 
I have seen this in Cambarus, Engeus, Axius, Gebia, Calo- 
caris, Callianassa, and Thalassina ; and it occurs, no doubt, in all 
