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ginous, with membranous margins which are fringed with many 

 jointed rays (Fig. 9). The extreme margin is ciUated and perfectly 

 circular, its diameter measuring 072 mm. Four muscles are attached 

 to each for the purpose of producing a vacuum in the sucker and thus 

 enabling the parasite to hold on securely to its host whilst feeding, 

 whilst ovipositing, or as claspers during copulation. 



The tail-plate at the extremity of the thorax is a flat, oval, bilobed 

 organ. Its use is primarily as a rudder. Some consider it to be an 

 organ of respiration. In the male it contains a portion of the 

 reproductory organs, which are called the testicles by some authori- 

 ties. In the female it has two well-defined oval black spots (one at 

 the base of each lobe of the tail-plate) (Fig. 12). They are called the 

 receptaculi by Claus, and their presence readily enables one to dis- 

 tinguish the female. Numerous spines and glands appear on its 

 surface ; some of the latter are very curiously provided with a tail- 

 like duct. Inside the margin of the lobes is a blood-channel. 



The Argulus has an armament of hooks and spines of varying 

 size and structure, the under surface of the carapace being studded 

 with them. All point in one direction — that is, to the tail portion. 

 There are some very curious spines on the under surface of the 

 joints of the foot-jaws, which are probably some special sense organs ; 

 some are bifid and trifid, and not unlike the scales of the lepidop- 

 tera. Numerous gland-cells exist on the surface of the integument 

 in addition to those on the tail-plate. 



The genital organs of Argulus are probably the most interesting 

 of all, and their position, structure, and method of copulation are 

 remarkable. 



The male genital organs are situated on the third and fourth pairs 

 of swimming-feet on both sides of the thorax, and are thus in 

 duplicate (Fig. ii). On the anterior margin of the first joint of the 

 fourth pair is a brown-coloured, conical tubercle of a horny nature. 

 Corresponding to this we find on the posterior margin of the first joint 

 of the third pair of feet a vesicle called the semen-capsule, filled 

 with a transparent fluid, apparently for fecundation. Previous to 

 copulation this fluid is opaque and darker than the surrounding 

 tissues. Five minutes after copulation this opaque matter becomes 

 absorbed, leaving a transparent sac. In the middle line of the 

 thorax and near to the base of the tail-plate is a dark purple- 

 coloured organ, the contents being granular. This is called the 

 semen bladder, and from it proceed two branches. The tail-plate, 

 as before mentioned, contains two brown-coloured patches or so- 

 called testicles in either lobe, but in what manner these and the 

 last-mentioned structures communicate with the male fecundating 

 organs is not very clear. 



The female organs comprise the ovary, the oviduct, the two 

 receptaculi, and the papillee. The ovary of the gravid female occu- 

 pies the whole of the ventral surface of the thorax. At puberty the 

 outer coat is covered with numerous pigment-cells of typical structure. 



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