Cirripedia, Barnacles. 83 



cipcs may 1)0 nuted as having rows of valves on the capituUun Table-case 

 whicli pass gradually into the small scales covering the peduncle. ^°- ^• 

 These scales appear to be the remains of a shelly armour covering 

 the peduncle wliich was more fully developed in certain extinct 

 genera, and is shown in the casts of the fossil Loricula and Tiirri- 

 lepas exhibited in this case. The genus Scalpellum is of interest 

 not only on account of the deep-sea habitat of many species and 

 the great size of some {Scalpellum rjujantcum), but also and more 

 especially because of the dvv'arf male individuals already alluded to, 

 which are found in this genus and in the related Ibla. In the 

 different species of Scalpellum three conditions are represented. 

 In some, all the individuals of a species are similar and hermaphro- 

 dite as in ordinary barnacles ; in others, as in Scalpellum peronii, 

 of which a specimen is shown, the large hermaphrodite individuals 

 have small males attached to them like parasites ; in others again 

 the separation of the sexes is complete and the larger individuals 

 are purely female. 



Most barnacles are hatched from the egg as actively swimming 

 larvae of a type which is found in many other Crustacea, and is 

 known as the Nauplins. They have three pairs of appendages, an 

 unsegmented body, and a conspicuous median eye. Like many 

 other " pelagic " animals the Nauplii of barnacles living at the 

 surface of the ocean often have long spines and outgrowths 

 from the surface of the body, which are probably of service in 

 keeping the animals afloat. A coloured drawing of one of these 

 spiny larvae is exhibited. In its later development the young 

 barnacle passes into a stage in which the body and limbs are 

 enclosed in a bivalved shell like an Ostracod. On account of this 

 resemblance the stage is known as the " Cijpris " stage, after one 

 of the genera of Ostracoda. After swimming about for some time 

 longer it attaches itself by means of its antennules, casts off 

 its bivalved shell, and gradually assumes the structure of the 

 adult. 



The Sessile Barnacles or Acorn-shells, forming the sub-order 

 Opeeculata (Pig. 18b), agree in most points of structure and 

 development with the stalked barnacles, but they have no peduncle. 

 The shelly plates of the mantle are, for the most part, soldered 

 together to form a cylindrical or conical case, the opening of which 

 is protected by four movable " opercular " plates. In a preparation 

 of Catophragmufi poli/merus here exhibited, names are attached to 

 those parts of the shell which are found (though often reduced in 

 number by coalescence) in all the typical Operculata, the " scutum " 



