THE CIRRI FED I A 117 



other Pedunculata and Operc.uluta. In the Acrothoracica (Aldppe) 

 also the adductor is ventral in position. 



The peduncle of the Pedunculata is provided with longitudinal 

 and oblique muscular fibres, and some of these may extend into the 

 mantle, but no definite muscles other than the adductor scutorum are 

 connected with the valves of the shell. In the Operculata Symmetrica, 

 however (not in the Asymmetrica), a pair of depressor muscles are 

 connected with the terga and two pairs with the scuta (Fig. 64, 

 m.d.t, ni.d.s}. 



Nervous System. The ventral nerve-chain is concentrated into 

 a single mass, within which, however, the outlines of five pairs of 

 ganglia may be made out. In the Pedunculata a pair of large 

 nerves originating from the anterior part of the cerebral ganglia 

 pass down the peduncle, and may perhaps represent the antennular 

 nerves. 



. Sense-Organs. Apart from the setae, supposed to have a sensory 

 function, on various parts of the external surface, and from such 

 doubtfully sensory structures as " Koehler's organ " in the pedun- 

 cular scales of Pollicipes, the chief organ of special sense persisting 

 in the adult is the nauplius-eye. This is deeply buried in the 

 tissues of the body, on the dorsal surface of the stomach, and may 

 be single (Pedunculata), or divided into two parts (Operculata). 

 In Lepas it consists of two pigment-cups, each containing a single (?) 

 cell, the inner surface of which bears a series of rodlets imbedded 

 in the pigment. The structure of the paired eyes in the Operculata 

 is not fully known, but it seems probable that they correspond to 

 the two halves of the Lepadid eye separated, and not to the 

 paired compound eyes of the Ci/pris larva. 



Reproductive System. The great majority of the Cirripedia are 

 hermaphrodite, and cross fertilisation is rendered possible by their 

 gregarious habits. 



The ovaries in the Pedunculata are lodged in the peduncle 

 (Fig. 67, Ov\ sometimes invading the mantle (ConcJwderma), and in 

 the Operculata they occupy the basal and, when fully developed, 

 also the parietal portions of the mantle (Fig. 64, ov). The paired 

 oviducts traverse the prosoma and open to the exterior at or near 

 the base ot the first pair of cirri. Just before reaching the exterior 

 each oviduct expands to form a genital atrium (described by 

 Darwin as an " acoustic organ "), with glandular walls within 

 which is secreted a sac or sheath for the reception of the eggs. 

 The extruded 3ggs contained in these sacs form the "ovigerous 

 lamellae " frequently found within the mantle-cavity, where they 

 are retained until hatching takes place. 



The testes lie for the most part in the prosoma (Fig. 64, c.t, 

 Fig. 67, T), extending, however, into the thoracic region and even 

 into the filamentary appendages and the bases of the cirri. 



