252 SCALPELLUM ORNATUM. 



the lines of growth, with that portion alone of the scutum 

 in S. vulgare, which lies under the curved ridge connecting 

 the umbo and tergo-lateral angle. The deep cavity in 

 which the male is lodged, is formed subsequently to the 

 preparatory furrow, simply by the gradual thickening of 

 the surrounding surface of the valve, more especially of a 

 ridge just above the pit for the adductor muscle, and of 

 another broad ridge just beneath the tergal margin. The 

 deepest part of the cavity lies parallel to the tergal margin 

 along the upper side, and here, in the older valves, the 

 preparatory furrow can by care be distinctly traced. In 

 conformity with the shape of the cavity, the orifice or notch 

 in the occludent margin of the scutum, is situated at the 

 point where the preparatory furrow sweeps round and 

 enters. I believe that the cavity is lined by membrane, 

 and that between the cavity and the body of the female, 

 there is a complex membranous layer, — a pouch or bag 

 being thus formed. An imaginary section of this pouch 

 (with the thickness of all the parts extremely exaggerated 

 and in a reversed position) is given in PI. VI, fig. 1 d'\ a 

 is the shell ; w the cavity, converted, as I believe, into a 

 pouch by, firstly, the delicate tunic (c) lining the sack of 

 the female ; secondly, a double layer (d) of corium ; and, 

 thirdly, by a special, rather thick membranous layer (5), 

 which thinning out round the cavity coats only part of 

 the under surface of the scutum. This latter membrane 

 I have not seen in any other Cirripede, and I believe it 

 is nothing but the tissue, here not calcified, which, in a 

 calcified condition, ordinarily forms the valves. On this 

 view, the males may be said to be lodged in pouches, 

 formed in the thickness of the valves. 



Concluding Bemarks. — The males from the absence of 

 a mouth (and no doubt of a stomach), must necessarily be 

 short-lived, and, I suppose, are periodically replaced by 

 fresh males. # In one instance, the remnants of the two 



* It is possible, though opposed to all analogy, that the females may be 

 short-lived, and breed only once, in which case the males would not have 

 to be periodically replaced. 



