MUSEUM OF COMPARATIVE ZOOLOGY. 307 
teen, thirty-two segments, and so on, until the whole surface of the egg 
is made of minute, polygonal cells (perimorula) No polar globules are 
emitted.* 
Twenty-four hours after the cleavage began, an egg was found in the 
gastrula-stage, as represented on Plate I. Fig. 3. The cavity is very 
small eompared with the size of the egg, and its orifice (g) is bounded 
by elliptical cells, which form a light-colored disk on the surface of the 
egg. The orifice apparently elosed a little later, and the further history 
of the cavity was not obtained. 
The yelk now shrinks away from its membrane in the vicinity of the 
light-colored disk, and becomes transparent and free from granules 
preparatory to the appearance of the parts of the embryo. 
The parts of the embryo which first appear are the abdomen, the 
labrum and cephalie disks, and the first three pairs of appendages. 
These appear almost simultaneously. A protuberance from the surface 
of the yelk, near the place where the gastrula opening appeared, is the 
rudiment of the abdomen. Another fold over against the first is the 
beginning of the formation of the labrum, and in front of this two disks 
appear, which are the first trace of the eyes and front part of the head 
of the embryo. 
The projection of the two folds which form the abdomen and labrum 
is such that the free ends are toward one another. Thus the abdomen, 
from the time of its earliest appearance, is bent forward underneath the 
breast of the future prawn. On each side of the labrum and abdomen 
are three lobes, which are the rudiments of the two pairs of antenne and 
the mandibles, The first pair are on a level with the labrum, the third 
pair with the end of the abdomen. All three pairs are simple. This is 
the nauplius-stage of the embryo.T 
* P. Mayer observed occasionally in fresh-laid eggs of Eupagurus ‘a sort of Rich- 
tumgsbliischen,” but he considers these cases abnormal, They were probably the 
result of disintegration of the egg (op. cit., p. 223). 
+ Joly's account of the order of appearance of the appendages of the embryo of 
Curidina, — first, the three pairs of thoracic legs (i. e. the maxillipeds), then the 
maxilla, mandibles, and antennæ, — is without doubt incorrect (op. cit., pp. 59, 60). 
In an abstract of a paper ** On the Development of the Crustacean Kmbryo, and. the 
Variations of Form exhibited in the Larve of 38 Genera of Podophthalmia " (Proc. 
Royal Soc, London, Vol. XXIV. p. 378. 1876), Spence Bate states his belief “that 
he has demonstrated that tho three pairs of mobile appendages in the eirripedal or 
Nauplius form of larva homologize with the eyes and two pairs of antennw, and not 
with the antenne and mandibles, as stated by Fritz Müller, Anton Dohrn, and 
others.” (!) It is to be hoped that the evidence will not long be withheld from 
publication, 
