EPIZOA. 



271 



developed upon the confluent extremities of a pair of obscurely jointed 

 tubular feet — the third thoracic limbs of the larva (/, /), — as in the 

 Lerneopoda of the shark*, the Achtheres of the perch, ^^. 116, and 

 the Tracheliastes of the chub. In the last-named parasite, which 

 may be found adhering to the fins of the Leuciscus cephalus in the 

 months of October and November, the head and thorax are confluent, 

 unless the segment to which the bases of the before-mentioned 

 feet are attached be held to represent the thorax. The abdomen 

 is, as usual, the largest segment. The mouth, ^^. 115, a, is a cir- 

 cular aperture, fringed with minute 

 short bristles ; on each side there is a 

 maxilla ( e, e), dentated at the inner 

 margin, and terminated by a bifid hook. 

 The antennje {f), are represented by 

 two short lancet-shaped processes, ter- 

 minated at the apex by a few extremely 

 short bristles. The most conspicuous 

 appendages of the head are, however, 

 a pair of mandibles {b, b), which con- 

 sist of two obscure joints, the second 

 of which has a bifid extremity ; the 

 outer division (c), is armed by a strong 

 curved spine, which is opposed to two 

 short straight spines ; the inner division {d), is tipped with four small 

 spines. Immediately behind the large tubular prehensile process is 

 a short rudimental extremity, supporting a moveable hook, which 

 is opposed, as in the mandibles, by two short spines. The muscular 

 system is sufiiciently conspicuous in the head of this Epizoon in the 

 form of distinct fasciculi of fine fibres (g\ 



In i\\e. Penella\, the head resembles a cauliflower, swelling out into 

 a globose group of slightly branched and obtuse wart-like processes, 

 which must have grown after the head had become imbedded in the 

 flesh of the fish to which it is attached. Two long tubular processes 

 or extremities are developed at the junction of the thorax with the 

 abdomen ; but their extremities are free, simple, slightly attenuated, 

 and obtuse. On the under surface of the body, in the interspaces of 

 these appendages, there are four pairs of simple, small, oval, flattened 

 feet ; their pointed extremities extend only half way to the sides of the 

 part of the body to which they are attached. The body is prolonged 

 beyond the ovisacs in the form of a tail, which is provided on each side 

 with a series of sixteen slender cylindrical appendages, close set in an 



Tracheliastes. 



* Prep. No. 286. A. 



t Prep. No. 286. 



