84 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



within the shell. The labrum is lost, as also are the great antenna?, 

 while the mandibles are reduced to a pair of small jaws (mn.) All 

 the thoracic appendages have become external, and are each provided 

 with a pencil of long bristles, and perform swimming movements by 

 giving sharp jerks in unison. A good deal of the internal organi- 

 zation is obscured by the presence of a considerable number of oil 

 drops (o. g.), but many points may be made out in living and in 

 Canada balsam specimens. One can still distinguish the Nauplius-eye 

 (Np. e.), while the compound eyes (c. e.) are now well developed, and 

 can sometimes be seen to have a continual twitching movement. 

 The shrivelled stomach (s.) appears as a red spot (bleached in 

 mounted specimens) in the front part of the thorax. A powerful 

 adductor muscle (ad. sc.) runs from one valve of the shell to the 

 other, and just in front of this is seen a kidney-shaped glandular 

 structure (rn. gl.), the function of which is not clear ; the same may 

 be said of a transparent oval sac on each side of the body near the 

 Nauplius-eye (Fig. 26). The thorax (th.) can now be completely 

 withdrawn within the shell by an important muscle (Fig. 24) ; when 

 protruded, the thoracic ganglionic chain (t. g. c.) can be seen as a 

 conical mass just above the bases of the appendages. The Cypris- 

 stage no longer feeds, and shows little or no reaction to light, and 

 seems to pass its time chiefly in sporting at the surface of the 

 water. 



The Cypris-stage of Balanus balanoides (Figs. 27 & 28) can be 

 distinguished by a number of points from the corresponding stage of 

 other Barnacles. Among the most readily recognized features are the 

 large size (I'll mm. in length), and the pitted markings on the shell 

 (Fig. 18). The shape, too, differs from that of other species found on 

 our coasts. The anterior and posterior portion of each half of the 

 mantle are reddish and marked by a number of minute chocolate 

 coloured spots, and towards the hinder end on each side of the thorax, 

 is usually (if not always) found an accumulation of minute greenish 

 yellow oil droplets (o. g.) The apertures of the fron to-lateral glands are 

 very small. (Compare Figs. 24 & 25 representing the immature Cypris- 

 stage of another species of Balanus which was obtained along with the 

 other by Messrs. Sinel and Hornell off Jersey). This Pupa is smaller 

 (0 -l 7 mm.) and more transparent than that of B. balanoides, and has 

 no markings on the shell ; the fronto-lateral apertures are tolerably 

 prominent. Another British species is shown in Fig. 26. It was 

 obtained in the surface waters of Plymouth in May, 1892 : I am 

 un'able to name even the genus of this form ; it may perhaps belong 

 to Chthamalus stellaius, which is excessively common in that district. 

 It has an elongated shape and undulating contours, and is almost 

 colourless ; it has a number of small reddish brown spots principally 



