TYPE ORUSTAOEA. 401 



system consists in Lepas of a syncerebrum and five or six 

 ventral ganglia, — of which the last is probably composed of at 

 least two fused ganglia, and a certain amount of fusion has 

 also probably occurred in the first. In Balanus the fusion 

 has reached its greatest extent, the entire ventral chain of 

 ganglia having fused to a single mass. The median unpaired 

 eye is usually represented, and in some forms rudimentary 

 lateral eyes are present, showing, however, a marked degen- 

 eration from the large compound eyes which occur in the 

 Cypris-like larva. 



As a rule the Cirrhipedia are hermaphrodite in accord- 

 ance with their sessile or parasitic life. The testes (Fig. 

 181, B, t) lie one on each side of the digestive tract, and the 

 vasa deferentia {vd) after dilating into seminal vesicles pass 

 to the long cirrus {cir) borne by the abdomen, at the tip of 

 which they open by a short common duct. The ovaries lie 

 in Lepas (Fig. 181, B, ov) in the stalk, and in stalkless forms, 

 such as Balanus, in the basal fold which corresponds to the 

 stalk, and the oviducts (od) passing upwards and then back- 

 wards open on the basal joints of the anterior thoracic ap- 

 pendages. Although hermaphroditism is the rule throughout 

 the order, yet in some cases small males have been found 

 which have received the name of " complemental " males. 

 These occur in the genus Ibla and in some species of Scalpd- 

 lum and live like parasites in folds of the mantle of the her- 

 maphrodite forms. In form they do not advance greatly 

 beyond the Cypris stage, and possess in addition to the anten- 

 nules only four pair of small thoracic limbs, the mandibles and 

 maxillae as well as the mouth being entirely wanting, while 

 the digestive tract is rudimentary. In other species of ScdL 

 pdlum, and in the genera Alcippc. and Cryptophialus, these 

 pigmy males are also present, but the forms in which they 

 live are no longer hermaphrodites but females, so that bi- 

 sexuality with sexual dimorphism occurs in these forms. 



It might be supposed from the general occurrence of bisexuality among 

 the Crustacea that these last cases represented the first stage in the dis- 

 appearance of the males, leading finally to hermaphroditism. Since, how- 

 ever, Aleippe and Cryptophiahis are the most degenerate of the Cirrhi- 

 peds so far discussed, it would seem that this is not the case, but rather 



