11. Pupa stage, on four times the scale of three previous figures. In this stage it crawls freely about in the sac 
of the mother. I, prehensile antenne with a disk-segment. There are no other appendages developed. 
oc, compound eye. The ventral surface between the sides of the carapace is formed of thin structureless 
membrane. On this surface, close to the posterior end, is a small orifice through which three pairs of 
bristles project, attached to a rudimentary abdomen. No mouth exists. 
12. Adult male on same scale as the last figure. The prehensile antenne now serve to fix the male, by a 
cement, to the female. a, orifice of sac. 
13-25. Development of Balanus. 
13-21. Balanus balanoides, from Hoek, Zur Entwickelungsgeschichte der Entomostraken. I. Embryologie 
von Balanus. Niederlandisches Arch. Zool., I1I., Taf. 111., 1V., 1876. 
13. Egg some time after fecundation. pe, polar cell? s, spermatozoa ? 
14. Later stage. The formative yolk (pp) has collected at the blunt pole of the egg and become sharply separated 
from the nutritive yolk (dp). 
15. The formative yolk has divided into four cleavage products, which enclose a part of the nutritive yolk at the 
centre of the egg. mc, nucleus of one of the cleavage spheres. § third cleavage sphere, the fourth being 
entirely concealed in the figure. 
16. Optical section of the same ata later phase. The formative yolk (47) has completely surrounded the nutritive 
yolk (dp), which has also split up into numerous parts. a, 5, folds in the blastoderm which are the com- 
mencement of the formation of the appendages of the embryo. 
17. More advanced stage from the dorsal side. The three nauplius appendages are seen. cp, dorsal shield or cara- 
pace. ct, cuticle shed by the embryo. ; 
18. Embryo nearly ready to hatch. 7b, labrum or proboscis. oc/, nauplius eye. w, hinder extremity. 
19. Nauplius larva, just escaped from the egg. 7, intestine. 
20. The same after the first moult. 7, frontal sensory thread. The frontal horns of the carapace, and many of 
the sete of the swimming appendages are shortened through a partial invagination. 
21. The dorsal spine in the process of evagination. 
22. Balanus larva from Naples before passing into the pupa stage, seen from below. I, anterior antenna. 
Through the transparent cuticle is seen the anterior appendage of the next stage, with the sucking-disk on 
the third segment whereby the pupa attaches itself. The mandibles of the adult are probably developed in 
the base of the third pair of nauplius appendages (III). IV, first pair of maxille. V, second pair of 
maxille. VI-XI, six pairs of thoracic biramous swimming-feet of the Cypris stage, corresponding to the 
five pairs of natatory feet of Copepoda, and the generative appendages of the following segment. fh, frontal 
horns of the carapace. g/, gland at base of frontal horn. This gland is connected with a hollow spine 
lying within the frontal horn, and its function is doubtful. ph, posterior horns of the carapace. oc, com- 
pound eye. 1, dorsal spine of abdomen. 2, ventral spine of abdomen. From Claus, Untersuchungen zur 
Erforschung der Genealogischen Grundlage des Crustaceen-Systems, Taf. XVI. fig. 1, Wien, 1876. 
23. About the same stage of a Balanus from Newport, R. I., profile view. From a sketch by A. Agassiz, August 
26, 1872. 
24. Cypris stage of a Balanus from Newport, R. I., reared from the stage of Fig. 23, August 26, 1872, profile view. 
Median and paired eyes are present as before. The carapace has become a bivalve shell, the two valves united 
along their dorsal margin. The anterior antenne are now furnished with a suctorial disk for attachment, 
in the centre of which is the opening of the duct of the antennary or cement gland. The second and third 
pairs of nauplius appendages have disappeared, unless a small papilla, the rudiment of the mandible of the 
adult, is a vestige of the third. The six posterior pairs of feet (VI-XI) have developed into long two- 
branched swimming-feet, replaced in the adult by the six pairs of cirrhi. £ abdominal portion of the 
body. From a sketch by A. Agassiz, August 26, 1872. 
25. Anterior antenna of Cypris stage of Balanus balanoides. d, suctorial disk by means of which the larva 
attaches itself. From Bate, On the Development of the Cirripedia. Ann. Mag. Nat. Hist., [2.] VIII, Pl. 
VIII. fig. 18, 1851. 
