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 antennae with a disk-segment. There are no other appendages developed. 

 c, 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 jjaire of 

 bristles project, attached to a rudimentary abdomen. No mouth exists. 



12. Adult male on same scale as the last figure. The prehensile antenna; now serve to fix the male, by a 



cement, to the female, o, orifice of sac. 

 13-25. Development of Balanus. 



13-21. Balanus balanoidcs, from Hoek, Zur Entwickelungsgeschichte der Entomostraken. I. Embryologie 

 von Balanus. Niederliiudisches Arch. Zool., 111., Taf. III., IV., 1876. 



13. Egg some time after fecundation. ^ c, polar cell ? s, spennatozoa ? 



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. nc, nucleus of one of the cleavage spheres, f, third cleavage sphere, the fourth beuig 

 entirely concealed in the figure. 



16. Optical section of the same at a later phase. The formative yolk (b I) has completely surrounded the nutritive 



yolk (dp), which has also sjilit up into numerous parts, a, b, folds in the blastoderm which are the com- 

 mencement of the fonnation 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, c t, cuticle shed by the embryo. 



18. Embryo nearly ready to hatch. ? 6, labrum or proboscis, oc?, nauplius ej-e. u, hinder extremit}'. 



19. Nauplius larva, just escaped from the egg. i, intestine. 



20. The same after the first moult. /, frontal sensory thread. The frontal horns of the carapace, and many of 



the setffi 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, vdih. the sucking-disk on 

 the third segment whereby the jiupa 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 maxilla;. V, second pair of 

 maxillffi. VI-Xl, six pairs of thoracic biramous swimming-feet of the C'ypiis stage, corresiiondiug to the 

 five pairs of natatory feet of Copepoda, and the generative appendages of the following segment, fh, frontal 

 horns of the carapace, g I, gland at base of frontal horn. This gland is connected with a hollow spine 

 lying within the frontal hoi'u, and its function is doubtful, jih, posterior horns of the carapace, oc, com- 

 pound eye. 1 , dorsal spine of abdomen. 2, ventral spine of abdomen. From C'laus, I'ntersuchungen zur 

 Erforschung der Genealogischen Grundlage des Crustaceen-.Systems, Taf XVI. fig. 1, Wien, 1876. 



23. About the same stage of a Balanus from Newpoit, R. I., profile view. From a sketch by A. Agassiz, August 



26, 1872. 



24. Cj'pris stage of a Balanus from Newpoit, 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 antennie are now furnished with a suctorial disk for attachment, 

 in the centre of which is the opening of the dtict 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 (^'I-XI) have developed into long two- 

 branched swimming-feet, replaced in the adult by the six pairs of cinhi. |, abdominal portion of the 

 body. From a sketch by A. Agassiz, August 26, 1872. 



25. Anterior antenna of Cypris stage of Balanus balannidfs. d, suctorial disk by means of which the larva 



attaches itself. From Bate, On the Development of the Cirripedia. Ann. Mag. Nat. Hist., [?.] VIII., PI. 

 VIII. fig. 18, 1851. 



