MORPHOLOGY OF CYCLOPS. 27 



TUE KlDNET. 



The organ (PI. III. fig. 7) to which this term applies has heen described by Huxley as " a 

 coiled tube with colourless contents." It is a simple tube lying at the sides of the carapace 

 in the region of the maxilla? and maxillipeds, just above the reflection of the pleura, into 

 which it does not extend. The numerous coils lying partially one over the other will bo 

 found, l)y careful focussing, to sliow the arrangement figured ; Iho shading is inserted 

 to guide the eye in following the coils. At (2) the tube bends horizontally inwards 

 behind the lower part of the dorsal flexor of the outer maxilliped ; it then bends down- 

 wards, forming a small irregular dilatation at the base of this limb, and finally opens into 

 a depression at the hinder and inner edge of the liml), between the extensor and the flexors 

 of the third joint. This course may be followed in transverse sections, and in specimens 

 of which the soft parts have been dissolved by ammonia. 



The coils are best seen in the living animal on its side, under a fairly high power ; the 

 horizontal part of the duct and its opening may sometimes he seen too in the live animal, 

 supine, under the right amount of pressure, with the limbs in suitable positions — a 

 matter rather of chance than skill. The other end of the tube, turning inwards at (1), is 

 seen in transverse sections to run horizontally parallel to the duct, and opens apparently by 

 a wide trumpet-shaped mouth into the coelom. The arrangement of the coils fia-ured is, I 

 believe, general in C. brevicornis, and occurs but slightly modified in some specimens at 

 least of C. tennicornis, C. coronatus, and 6'. serridatus. The histology of the tube is very 

 simple, a cuticulized tube, suspended by connective tissue in which I have been unable 

 to detect any specialization. This organ, first described as opening near the mouth, and 

 probably a poison-gland, by Zenker, was identified by Clans and Leydig with the " Sclia- 

 lendriise " of Phyllopods ; Glaus showed, in successive papers, that this gland opened on 

 the base of the outer part of the second maxilla in Phyllopods proper, and behind the 

 single maxilla in Cladocera ; he also showed its opening at tlie base of tiie outer maxilliped 

 in some parasitic Copepoda. But I believe that this is the first demonstration of its course 

 and aperture in the swimming Copepods. Among the Calanidce a similar gland is 

 known in the freshwater Diaptomus, but has been denied to marine Copepoda. Sections 

 of Calamus finmarcliicns. Leach, and a Po)ttelUna have revealed it in its proper position, 

 but much simpler, indeed a simple loop, of which one end opens on the outer maxilliped. 

 I have also found it in the "youngest Cye/c^w-stage " of Canthocumpiuii,io wliich it 

 has been alternately ascribed and denied, and in Sapplih^inu. 



Clans describes in the Nauplius CopejDod larvae {Diaptomus, Cyclops) a similar tube 

 forming a loop, of which the two ends lie in the region of the second liml) {at'). This 

 is the case; the loop extends far back, about two thirds the length of flie Nauj)lius, 

 lying below the dorsal retractors of the limbs. The two ends lie close together, one 

 coiled and the other nearly straight, in the base of the antenna on the ventral side, 

 internal to and ventrad of the "masticating hook." In the youngest Nauplius [ Avas 

 uncertain of an aperture; in the next stage with one pair of appendages added, tlu; 

 straighter limb in the antenna abuts clearly against the surface, and possibly opens 

 there ; while the other coiled limb is continued back again to an irregularly triangular 

 mass of protoplasm, vacuolated, and containing refractive globules (PI. III. fig. 9). 



4* 



