13. 
14. 
16. 
17. 
18. 
19: 
24. 
Egg during the cleavage process. The cleavage is superficial. pc, a body supposed to be a polar cell, although 
its origin from the germinative vesicle was not ascertained. It is present at the time the egg is laid. 
Gastrula stage in longitudinal optical section. gm, gastrula invagination. The gastrula mouth seems to 
close completely at a later stage. hy, hypoblast. ep, epiblast. ms, mesoblast. The mesoblastic cells 
are withdrawn from the surface of the blastosphere into the interior just before the gastrula invagination 
takes place. gem, two of the four cells which subsequently are split into eight and pass into the interior 
of the embryo, take a position under the hypoblast, and develop into the genital organs. These genital 
cells were distinguishable before the cleavage was completed. dp, deutoplasm. 7, cephalic plate, from which 
the supra-cesophageal ganglion and eye are developed. 
. Embryo in the nauplius stage, ventral view. I, anterior antenne. II, posterior antenne. These first appeared 
in an earlier stage as simple buds, before the first and third pairs of appendages began to form. They are 
now two-branched. III, Mandible. The mouth (m) and esophagus (oes) are forming from an invagi- 
nation of the epiblast. The cesophagus is short and abuts blindly against the intestine (7). 
Later stage, ventral view. Behind the mandibles is seen a maxillary segment (9), although no trace of the 
maxille has yet appeared. Behind the maxillary segment are two thoracie segments with slight rudiments 
of their appendages (VI, VII). 7, cephalic plate in optical section. 7, mid-gut, the product of the hypo- 
blastic germ-layer. The cesophagus (0¢s) is longer, but still terminates blindly. The place where the 
rectum is to arise is indicated by a thickening of the body-wall at the posterior extremity. 
Later stage from ventral side. Four pairs of feet (VI- 1X). The two maxillary segments are united, and show 
no appendages yet. On the outer side of the second antenne is a protuberance (1) connected with the 
development of a sensory seta which occupies the corresponding part in the adult. The genital cells have 
divided into a right and left portion. The shell («) begins to appear as a fold of the dorsal integument in 
the maxillary region. 
The next stage, from below. The fifth foot (X) has appeared. The four anterior feet are becoming differ- 
entiated into an inner branch, outer branch, and branchial appendage (in the third foot, these parts are 
indicated by the characters VIII, VIII’, and 6r’’). The first maxilla (IV) has appeared. 
Embryo in the next following stage, lateral view. Observe the dorsal flexure of the body. 7, labrum. The 
second antenne (II) begin to show segmentation in both their branches. The second maxilla (V) has now 
made its appearance. This is commonly said to be wanting in the adult Daphnide@, but persists in a rudi- 
mentary condition in adult Moina, according to Grobben. All five pairs of feet have outer branches, except 
the first (VI), the single branch here corresponding to the inner branch of the other legs. Near the origin 
of the shell there is seen a group of cells (A) higher than their neighbors and furnished with larger nuclei. 
These go to form the dorsal organ. +, shell gland, as yet unprovided with an outlet, and probably developed 
from the mesoblost. The cephalic plate, at a period earlier than this, separated into an anterior portion (7) 
and a posterior portion (n”). The former develops into the brain proper (in the stage figured it has 
not yet become freed from the integument), the latter forms the retina of the eye. This has already 
separated from the surrounding epiblast which closes over it and develops into the compound eye. This 
eye is a paired structure at its first appearance. a, anus opening into the invagination of the epiblast 
which forms the rectum. 7, rudiment of the large posterior sensory seta. 
. Next stage, from below. The mandible (III) now shows a division into a palp and masticatory portion. 
. Later stage, from below. y, primary sensory seta on first antenna. The pigment is forming in the eye. In 
the median line is seen a furrow, widening posteriorly, formed by an invagination of the epiblast which 
makes the nerve-cord. The mandible (III) has lost its palp. 
. Embryo shortly before hatching, lateral view. The embryo has now essentially the characters of the adult, 
excepting the secondary sexual characters. vv’, olfactory sete. h, heart. About two days and a half are 
consumed in the development of the embryo. The dorsal organ is become reduced to a rudiment at the 
time of hatching, and is not found in the adult Moina rectirostris. In M. paradoxu, on the contrary, it 
persists throughout life. 
. Young Sida crystalvina at the time of quitting the brood-cavity of the mother, lateral view. A, provisional 
dorsal organ. This is the homologue of the dorsat organ in other Cladocera. A’, unpaired horseshoe-shaped 
dorsal organ. A”, paired dorsal organ. ‘y, shell gland. y, primary sensory seta.  »’, olfactory sete. 
From Grobben, Ibid., Taf. XVI. fig. 56. 
Leptodora hyalina. Larva just escaped from the winter egg, seen from below. The body shows no trace of 
segmentation. I, first pair of antenne. II, second pair of antenne (only the basal portion is represented 
on the left-hand side of the figure). III, third pair of appendages, representing the mandibular palpi. In 
the adult the mandibles are destitute of a palpus, as in other Cladocera. Behind the third pair of append- 
ages are seen the rudiments of the six pairs of feet of the adult in the form of small buds. oc/, ocellus, 
which persists in the adult. The adult form is gradually attained after the third moult. While the young 
developed from the winter eggs thus undergo a postembryonal metamorphosis, the summer eggs develop 
without metamorphosis, as is the case with most Cladocera. No ocellus is present at any stage in the 
development of the summer eggs. From G. O. Sars, Om en dimorph Udvikling samt Generationsvexel 
hos Leptodora. Forhandl. Vidensk.-Selsk. Christiania, Aar 1873,Tab. I. fig. 1. 
