122 THE VOYAGE OF H.M.S. CHALLENGER. 



characters, — as, for instance, the mouth-organs and feet, — these so-called species differ 

 from one another very little or not at all, the only distinctions being in the form and 

 proportions of the various parts of the body, and sometimes in the structure of the 

 antennae. Many of the described species are doubtless distinct and well marked, but I 

 cannot resist the conclusion that not a few have been founded on variable and uncertain 

 characters, — the form and proportions of the abdomen and cauctal stylets, for instance, 

 often varying very considerably amongst specimens which, as it seems to me, ought to 

 be referred to a single species, perhaps at different stages of growth or of slightly different 

 race. Between the two sexes there is usually a marked difference of form and colour, 

 the male being generally of a broadly ovate shape, without any distinct constriction or 

 line of separation between abdomen and thorax, and being, moreover, often highly 

 iridescent or opalescent ; the females, on the other hand, are devoid of colour, or nearly 

 so, and the abdomen is generally much narrower than the cephalothorax, and separated 

 from it by a distinct constriction. The abdomen is five-jointed in both sexes ; the 

 cephalothorax usually also five-jointed, but occasionally the first segment is incompletely 

 (or altogether) divided so as to form a sixth segment. There may be slight sexual dif- 

 ferences in the anterior antennae, and the posterior antennae are usually more robust and 

 more strongly armed in the male than in the female. The mouth-organs are small and 

 crowded together, consisting of a stout falciform mandible which has ciliated margins but 

 no teeth ; a subquadrate, sparingly setiferous maxilla, and two pairs of foot-jaws, — the 

 anterior quite rudimentary, small, and subtriangular, the posterior stouter and simply 

 unguiculate at the apex. The anterior antennae are usually short and five- or six-jointed, 

 more or less setiferous, and nearly alike in the two sexes ; the posterior are larger, stout, 

 prehensile, and strongly clawed ; in the female usually more slender and with weaker 

 armature. The eyes are complex, consisting of a small, median, "unpaired" eye, 

 ■somewhat vesicular in appearance, and of two much larger "paired" or "lateral" eyes, 

 each of which is composed of an anterior conical lens and a posterior more or less distant 

 vitreous body, with which is connected a long, fusiform, and variously-coloured pigment 

 body. 



The nervous system, owing to the considerable size and frequent glassy transparency 

 of the animals, is much more plainly visible than in most Copepocla, and consists of a large 

 central ganglion lying a little behind the eyes, and giving off numerous branches to the 

 limbs, viscera, and tegumentary structures. 



The alimentary apparatus — stomach, intestine, and liver — and the generative organs in 

 both sexes occupy a large part of the body- cavity, but call for no special remark here. 

 Indeed in spirit-hardened specimens the internal structure becomes almost totally 

 obscured and unfitted for minute examination. Haeckel has proposed to divide the genus 

 Saphirina, into two sub-genera, — Pyromma (or Saphirina proper), and Cyclnomma (or 

 Saphiridina) , the following being the characters on which the separation is based. 





