COMPLEMKNTAL MALE. 233 



there are four little calcareous beads (as mav be known 

 by their dissolving with effervescence in any acid, and 

 breaking easily under the needle) ; these are the ^ths of 

 an inch in their larger external diameter ; they are rather 

 deeply imbedded in the outer integument, and taper a 

 little downwards ending in a concave terminal point, into 

 which a minute tubulus enters, like those passing into 

 and through the valves of ordinary Cirripedia : along the 

 axis of imbeclment, they are often ^ths of an inch in 

 length. These calcareous beads or rudimental valves are 

 seated in pairs, at the two ends of the flattened animal, 

 so that when the animal is laid on one side, the upper 

 bead in each pair exactly covers and hides the lower one. 

 The outer integument is composed of chitine, as may be 

 inferred from boiling caustic potash having no effect on 

 it ; the upper part is thicker than the imbedded portion 

 and is wrinkled transversely; it is covered with minute 

 spines n^oooths of an inch in length, either single or in 

 groups of two and three, (PL V, fig. 14.) This outer 

 tunic is lined by corium, sometimes slightly mottled 

 with dull purple; and this by delicate, longitudinal, 

 striaeless muscles, running from the base up to the under 

 edge of the orifice ; these longitudinal muscles are crossed, 

 at least, in the upper part, by still finer transverse muscles. 

 Thorax and Abdomen. — When the external integument 

 is cut open, the thorax (PL V, fig. 13) is found lodged 

 within an inner sack or rather tube, extending from near 

 the bottom of the animal, up to the external orifice. The 

 whole thorax is sometimes forced through the orifice, owing 

 perhaps to the action of the spirits of wine and conse- 

 quent endosmose, and is thus well displayed without dis- 

 section. The thorax tapers a little, is much flattened and 

 straight ; its length ; together with the terminal abdominal 

 lobe, is about 5 §oths of an inch ; it is formed of very 

 thin, most finely hirsute membrane, transversely wrinkled 

 and so extensible, that when everted by the internal 

 muscles being seized, it stretches to twice its former 

 length ; in this condition, five transverse articulations are 



