ARTHROPODA 275 



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 



