13. 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 ascertaiued. It is present at the time the egg is laid. 



14. Gastrula stage in longitudiual optical section, g m, gastrula invagination. The gastrula mouth seems to 



close completely at a later stage, hy, hypoblast, ep, epiblast. vis, mesoblaat. The mesoblastic cells 

 are withdrawn from the surface of the blastosphere into the interior just before the gastrula invagination 

 takes place, g e n, two of the four cells which subsequently are split into eight and pass into the interior 

 of the embryo, take ^ position under the hypoblast, and develop into the genital organs. These genital 

 cells were distinguishable before the cleavage was completed, dp, deutoplasm. jj, cephalic plate, from which 

 the supra-oesophageal ganglion and eye are developed. 



15. Embryo in the nauplius stage, ventral view. I, anterior antennae. II, posterior antennae. 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. Ill, Mandible. The mouth (m) and oesophagus (oes) are forming from an invagi- 

 nation of the epiblast. The oesophagus is short and abuts blindly against the intestine {(). 



16. Later stage, ventral view. Behind the mandibles is seen a ma.\illary segment (i?), although no trace of the 



maxillae has yet appeared. Behind the maxillary segment are two thoracic segments with slight rudiments 

 of their appendages (VI, VII). i), cephalic plate in optical section. /, mid-gut, the jiroduct of the hypo- 

 blastic germ-layer. The oesophagus (o e 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. 



17. Later stage from ventral side. Four pairs of feet (VI - IX). The two maxillai-y segments are united, and show 



no appendages yet. On the outer side of the second antennte is a protuberance (i) 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 (k) begins to appear as a fold of the dorsal integument in 

 the maxillary region. 



18. 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 Vlll, VIII', and b r'"). The first maxilla (IV) has appeared. 



19. Embryo in the next following stage, lateral view. Observe the dorsal flexure of the body. I b, la brum. The 



second antenna (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 Daphnidce, 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 {\) higher than their neighbors and furnished with larger nuclei. 

 These go to form the dorsal organ, y, shell gland, as yet unprovided with an outlet, and probably developed 

 from the raesoblost. The cephalic plate, at a period earlier than tliis, separated into an anterior portion («') 

 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 lias already 

 separated from the surrounding e]iiblast which closes over it and develops into the compound ej-e. This 

 eye is a paired structure at its first appearance. a, anus ojiening into the invagination of the epiblast 

 which forms the rectum, ir, rudiment of the large posterior sensory seta. 



20. Ne.xt stage, from below. The mandilile (III) now shows a division into a palp and masticatory portion. 



21. Later stage, from below, v, 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. 



22. Embryo shortly before hatching, lateral view. The embryo lias now essentially the characters of the adult, 



excepting the secondary sexual characters, v', olfactory seta;, 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 rcclirostris. In M. paradoxu, on the contrary, it 

 persists throughout life. 



23. Young Sida crijstaUina at the time of quitting tlie brood-cavity of the mother, lateral view. \, provisional 



dorsal organ. Tliis is the homologue of the dorsal organ in other Cladocr.rn. \', unpaired hoi-seshoe-shaped 

 dorsal organ. K", paired dorsal organ. y, shell gland. v, primary sensory seta, y', olfactory setae. 

 From Grobben, Ibid., Taf. XVI. fig. 56. 



24. Leptodara hyalina. Larva just escaped from the winter egg, seen from below. The body shows no trace of 



segmentation. I, first pair of antennae. 11, second pair of antennae (only the basal portion is represented 

 on the left-hand side of the figure). Ill, third pair of appei\dages, representing the mandibular palpi. In 

 the adult the mandibles are destitute of a palpns, as in other Cladoccra. Behirnl the thiiil pair of append- 

 ages are seen the rudiments of the six pairs of feet of the adult in the form of small liuds. ocl, ocellus, 

 which pei-sistsin the adult. The adult form is gradually attained after the third moult. Wliile the young 

 developed from the winter eggs thus undergo a postembryonal metamorphosis, the summer eggs develop 

 witho\it metamorphosis, as is tlie case with most Cladoccra. No ocellus is present at any stage in the 

 development of the summer eggs. From G. 0. Sars, Oni en dimor|)li Udvikling samt Generationsvexel 

 hos Lcptodora. Forhandl. Vidensk.-Selsk. Christiania, Aar 1873, Tab. I. fig. 1, 



