14. Later stage (protozoéa). The carapace has increased in size. Compound eyes and frontal sense organs (f) have 
appeared, and the appendages (IV-VII) which before were functionless rudiments have developed into 
biramous swimming organs. The mandible has become reduced to a cutting blade without palpus. The 
hinder portion of the body has greatly increased in size, and behind the seventh pair of appendages is the 
indication of a number of somites. 
15. Mouth parts of the same, seen from below. The labrum (7 4) is produced into a prominent spine. 
16. Paired eyes of a little older larva. 
Norer.— Although the stages represented in the preceding figures were captured free-swimming on the ~ 
surface of the sea, and no connection directly established between the several stages or with the parent, 
there is no reason to doubt the correctness of Miiller’s identification of the forms as young stages of Peneus. 
17-21. From Claus, Untersuchungen zur Erforschung der Genealogischen Grundlage des Crustaceen-Systems, 
Taf. I1., II., Wien, 1876. 
17. Protozoéa stage of Peneus. 14mm. long. oc, ocellus. oc, paired eyes under the carapace, as in adult of 
genus Alpheus. jf, frontal sense-organ, similar to that of Phyllopoda. Behind the second maxillipeds ( VII) 
are six free thoracie segments. Under the cuticle of the first of these are seen the rudiments of the third 
maxillipeds (VIII). The abdomen (a) has no free segments yet, but under the skin can be seen the 
segmentation which causes the six abdominal somites of the next stage. 
18. Six thoracie somites and abdomen of a somewhat larger larva, zoéa form. The five anterior somites are now 
free, the sixth is not yet separated from the telson. It appears that the somites of the thorax and abdomen 
develop in regular succession from before backwards. The third maxilliped (VIII) is now a free bilobed 
bud, and behind it are seen the rudimonts of the following five pairs of thoracic feet. In the abdominal 
section of the body the last pair of limbs is apparent as a small bilobed process (XIX) on the sixth somite, 
and perhaps the slightest trace of the other five pairs is already perceptible. 
19. Older zoéa form of the same. The paired eyes are now freed from the carapace and mounted on long stalks. 
The five posterior pairs of thoracic appendages (those of the left side have been removed in the figure) have 
developed into prominent biramous sacs, while the third maxillipeds (VIII) are furnished with sete on 
each branch. The abdomen has become very long, the telson is separated from the sixth somite by a moy- 
able joint, and the posterior appendages (XIX) have assumed the shape of powerful swimmerets. The second 
antenn still serve as locomotive organs, in which office the muscular abdomen now assists. The five 
anterior abdominal somites have not yet developed appendages, at least to any functional degree. The 
development of the sixth abdominal appendages thus anticipates the development of the anterior pairs, 
probably on account of their functional importance as swimming organs. 
20. Schizopod or Mysis stage of a Peneus. 16mm long. As in the adult Mysis, the biramous thoracic feet now serve 
as swimming organs. All the abdominal limbs are present. The first antennw have lost their long sete, 
and grown an inner branch which becomes the inner flagellum of the adult appendage. The second an- 
tenne have resigned their locomotive office, and their outer branch has become reduced to the antennal 
“*scale” (1I/). The nauplius eye has disappeared, and mandibular palpi have developed. The transition 
from the Mysis stage to the adult is easy, the most marked change consisting in the reduction of the exter- 
nal branches of the five pairs of ambulatory appendages to rudimentary structures. 
21. Telson of the same stage. 
