Miscellaneous. 127 
as to whether she would have continued throughout her life to 
produce only females, or whether, at a more advanced age, her 
progeny would have been males, as was seen in the colony of 
Lrigona clavipes, mentioned above. In any case the non-simul- 
taneous production of individuals of the two sexes in one and the 
same colony points, in certain species of Meliponids, to the indis- 
pensable intervention of cross-fertilization, the advantages of which 
are well known to naturalists.—Comptes Rendus, t. exx. no. 5 
(February 4, 1895), pp. 273-275. 
On the Development of the Body in the Prawn (Palemon serratus, 
Fabr.) and the Crayfish (Astacus fluviatilis, Gesn.). By Lovis 
Rovte. 
For several years past I have prosecuted researches upon the 
development of the two crustaceans mentioned in the title of this 
note. The facts that I have observed are for the most part known; 
but several of the principal among them have not been described 
with great accuracy, and the interpretations that have been given 
of them seem to me to be incorrect. 
The ovum of these animals is chiefly composed of food-yolk : the 
formative yolk, at the moment of fertilization, collects into a little 
cicatricle, which alone produces all the elements of the embryonic 
economy. Contrary to what happens in the case of Porcellio, to 
the embryogeny of which I have devoted a recently published 
memoir *, the cicatricle does not commence by surrounding the 
entire ovum, to give rise afterwards to the appendages ; it develops 
on the spot and increases slowly, while giving rise in succession to 
the organs and the paired limbs. The ovum of Porcelliois globular ; 
the young embryo is itself spherical from the very first ; it subse 
quently elongates, increasing in size principally in the direction of 
the future longitudinal axis, and thus arrives at its definitive con- 
dition. The case is different both in the prawn and in the crayfish, 
At the very commencement of the embryonic development of these 
latter forms the cicatricle divides, following a plane almost tangen- 
tial to the surface of the ovum, into two superimposed parts. This 
cleft commences as a superficial depression, which extends across 
and sinks little by little into the cicatricle, dividing it in such a 
way that the latter, instead of remaining full and compact, appears 
divided into two halves, one of which is folded back beneath the 
other. ‘This arrangement persists, while the cicatricle increases in 
size, giving rise to the appendages and the organs; the halves 
enlarge and preserve their relations, one of them being tucked 
beneath the other. Finally, when the development is concluded 
and the body formed, the latter lies bent double ; the portion folded 
back corresponds to the abdomen, and the other to the cephalo- 
thorax. At the moment of hatching the curvature is effaced by 
the straightening of the whole, and the abdomen, assuming its 
* “Etudes sur le développement des Crustacés.”—lre Partie; re 
Mémoire: “Etude sur le développement du Cloporte (Porcellio scaber, 
Leach).” Annales des Sciences naturelles, Zoologie, 1894. 
