340 THE INVERTEBRATA 



process towards the mouth and a large, uniramous, foUaceous 

 palp, and the maxillules, simple structures with a fringe of strong 

 bristles on the notched median edge. A pair of simple, hairy lobes, 

 united by a median fold, which shut in the mouth and its appendages 

 from behind, represent the maxillae. The six pairs of thoracic limbs 

 or cirri have each two long, many-jointed, hairy rami, curled towards 

 the mouth. They are successively longer from before backwards. A 

 couple of filamentous epipodites ("gills") stand on the protopodite 

 of the first pair. Behind the cirri stands a long median ventral penis, 

 and behind this again is the anus, with a pair of vestigial /mit^/ rami. 



The animal feeds by thrusting out the cirri through the mantle 

 opening and withdrawing them with a grasping motion, whereby 

 particles are gathered from the water. If it be molested the motion 

 ceases and the valves are drawn to. The alimentary canal has an 

 oesophagus (stomodaeum) directed forwards from the mouth to the 

 long wide stomach which bears several coeca around its commence- 

 ment and tapers behind into an intestine. Complicated maxillary 

 glands open on the maxillae. There is no heart or system of blood 

 vessels. The nervous system has a suboesophageal ganglion, and 

 a separate ganglion for each pair of cirri behind the first. 



Lepas is hermaphrodite. The ovaries lie in the peduncle and the 

 oviducts open on the bases of the first pair of thoracic limbs, much 

 further forwards than is usual in Crustacea^ The testes are branched 

 tubes which lie at the sides of the alimentary canal and in the basal 

 parts of the cirri. Each vas deferens enlarges into a vesicula seminalis 

 whose duct joins that of its fellow in the penis. Impregnation takes 

 place by the penis depositing a mass of spermatozoa on either side 

 of the mantle cavity of a neighbouring individual, near the opening of 

 the oviduct. It is possible that isolated individuals may be self- 

 fertilized. The ova undergo their early development within the mantle 

 cavity of the mother attached in a flat mass, the ovarian lamella, by 

 a glutinous secretion manufactured by the terminal enlargement of the 

 oviduct, to a fold of the mantle which projects on each side from 

 near the junction with the body and is known as an ovigerous frenum. 



The young are set free as Nauplii, characterized, as are those of 

 nearly all cirripedes, by a pair of lateral frontal horns, on each of 

 which opens a unicellular gland (see Fig. 247). These are processes 

 of a dorsal shield which in later stages acquires other spines. After 

 several moults the larva suddenly passes into the so-called Cypris 

 stage. It is now enclosed in a bivalve shell with an adductor muscle, 

 and possesses a pair of compound eyes. The antennules of this stage 

 possess near their ends a disc on which opens the cement gland. The 

 antennae have disappeared. There are six pairs of biramous thoracic 

 limbs and a small abdomen of four somites. The Cypris larva becomes 



