IV FAMILIES OF PEDUNCULATA 87 
than bags of spermatozoa, but they possess to varying degrees 
the ordinary organs of the adult in a reduced condition. The 
male of S. peronii (Fig. 55, A) retains the shape and skeletal plates 
of the ordinary form, and differs chiefly in its reduced size; but 
the more common condition is exhibited by the male of WS. 
vulgare (Fig. 52, A), where the scutes are reduced to vestiges 
round the mantle-opening, and almost the whole of the body is 
occupied by the greatly developed generative organs. (3) In 
a few species, e.g. S. velutinwm and S. ornatum, the individuals 
are purely dioecious, being either females of the ordinary 
structure resembling the hermaphrodites of the other Lepadidae, 
or dwarfed males resembling closely the complemental males 
described above for S. vulgare. 
The nature and derivation of these various conditions will be 
discussed when the parallel cases found in 
Ibla and among the Rhizocephala have 
been described. 
The remaining genus of the Polyas- 
pidae, also characterised by the presence of 
numerous skeletal plates on the capitulum, 
is Lithotrya (Fig. 56), which bores into 
rocks and shells, and is an inhabitant of 
the warm and tropical seas. 
The peduncle of the full-grown animal 
is completely imbedded in the rock or shell 
to which it is attached, and at the basal 
end of the peduncle is situated a cup com- 
posed of large irregular calcified pieces. 
This cup is, however, not formed until the 
animal has ceased to burrow. The excava- 
tion of the substratum is effected by means We &: 
of a number of small rasping plates which Pere ee se 
cover the peduncle, the whole being set in cup; @, carina; R, ros- 
: - irund s) Ssuscutum 3) 7. 
motion by the peduncular muscles. henamnee, UNE EEID 
Fam. 2. Pentaspidae— In this family 
are placed a number of genera, and among them the common 
Lepas, the species of which possess typically five skeletal plates, 
viz., a Carina and a pair of scuta and of terga, the peduncle being 
naked. These forms are a later development of Cirripede evolu- 
tion, and did not come into existence till Tertiary times. Some 
