BRANCHIOPODA. 199 



indistinctly lobate, and on the three or four following, they are 

 unlobed. The thoracic shield (s) and the furcal processes have 

 increased considerably in size. As important new rudiments, we 

 have those of the paired eyes, which are situated dorsally above 

 and behind the jSTauplius eye, and in which the deposition of 

 pigment has commenced These rudiments and those of the 

 developing optic ganglia become more and more distinct during 

 the subsequent stages. 



At the fifth stage, there are nine distinctly lobate pairs of limbs, 

 a tenth rudiment indistinctly lobate, and four following these not 

 as yet lobate. Six more rudiments of segments are discernible 

 behind these. At this stage, the formation of the heart and the 

 branching of the liver by means of secondary diverticula progress 

 gradually. In the later stages which succeed one another through 

 numerous moults, the form of the adult is gradually approximated 

 by the appearance of fresh segments and limbs, by the increase 

 of the dorsal shield, which gradually covers almost the whole of 

 the dorsal region, and by the lengthening of the furcal processes. 

 At the same time a degeneration of the Nauplius limbs takes place, 

 the first antenna remaining as a small two-jointed stump, and the 

 second as a still smaller unjoin ted vestige ; of the mandibles, only 

 the basal joint is retained with its now strongly-developed masti- 

 catory blade. The distal part of this latter limb is visible in the 

 later larval stages as a gradually diminishing mandibular palp, which 

 finally disappears. This degeneration of the limbs is accompanied 

 by a change of the method of progression. In the first stages, the 

 larva jerks itself forward by the powerful strokes of the second 

 antennae, but now it moves more regularly by the gentler swimming 

 action of the numerous rowing limbs. 



The above description applies to Apus cancri/ormis. The develop- 

 ment of Apus produdus, made known to us by Brauer (JS'o. 18), 

 is quite in agreement with the above account. The egg, however, 

 is here considerably larger and the development more abbreviated. 

 The number of moults and of separate ontogenetic stages is smaller. 

 The second antennae, as early as the fourth stage, cease to act as 

 rowing organs, and at the sixth stage are greatly degenerated. The 

 MetanaupUus which hatches out of the egg has not only a large 

 number of segments, but already shoAVS the rudiments of the j^aired 

 eyes. 



The Metanauplius of Brancliijjus is somewhat longer, and the 

 thoraco-abdominal section of the body is more sharply separated from 



