ARTHROPODA 27 
ut 
have an excretory function, and if their inner end opens into 
a genuine coelomic cavity, they would satisfy the conditions of 
a nephridium and form an interesting transition between these 
widely distributed excretory organs and the shell gland of 
other Entomostraca. 
The existence of special respiratory organs is a matter of 
some uncertainty, certain processes at the base of the thoracic 
legs in Lepas, and on the inner surface of the mantle in Balanus, 
have been regarded as branchiae by some authorities, but their 
precise function seems doubtful. 
The nervous system of Lepas is composed of a supra-oeso- 
phageal ganglion, connected by commissures of considerable 
length with a ventral chain. This usually comprises five 
ganglia, the fifth is larger than the others and gives off two 
pairs of nerves, hence it probably represents the fusion of two 
primitively distinct ganglia. In the Balanidae the whole 
ventral nerve cord has fused into a common nerve mass. The 
supra-oesophageal ganglion gives off nerves to the stalk, to the 
mantle, and to the eyes; the mouth appendages and the first 
pair of thoracic limbs are supplied from the infra-oesophageal 
ganglion, The only sense organs which are definitely known 
are a pair of rudimentary eyes, which have fused together in 
Lepas, but are distinct in Balanus. 
The Cirrhipedia are peculiar amongst Crustacea, in that 
with few exceptions they are, as is frequently the case with 
sessile animals, hermaphrodite (Fig. 163). The testes form a 
branched gland upon each side of the alimentary canal; the 
numerous caeca of this gland unite into a vas deferens which 
dilates into a vesicula seminalis on each side of the body, the 
two vasa deferentia unite into a single ductus ejaculatorius 
which traverses the penis. The spermatozoa are motile, a 
condition not otherwise met with in the Crustacea except 
amongst the Ostracoda, and then only when they have entered 
the female ducts. 
The ovaries are very racemose glands, situated in the 
Lepadidae in the upper end of the stalk, in the Balanidae 
between the membranous or calcareous base of attachment 
and the mantle (Fig. 162). The oviducts, one on each side of 
the body, pass up towards the first thoracic limbs and open 
