292 ME. GEOEGE M. THOMSON ON A FEESHWATEE 



The five pairs of pleopocla (PI. XXV. fig. 4) on the first to the fifth abdominal segments 

 are all of a similar form in the females. Each consists of a subquadrate basal joint, the 

 outer portion of which appears almost as if articulated on to the rest. Near the outer 

 angle is the large multi-articulate exopodite, which forms an apparently more perfect oar 

 than the corresponding organ on the thoracic legs. Each is formed of numerous short 

 joints carrying several long plumose setse. On the inner side of the base is a small 

 oblong plate like a rudimentary branchia — the endopodite. In going back from the first 

 to the fifth segment, this endopodite diminishes in size. 



In the males the first pair of pleopoda (PI. XXV. fig. 5) have the exopodite normal, 

 but the endopodite developed into a lamelliform plate which projects inward (figs. 6 

 and 6 a). This plate appears to be furnished with a duct which opens near its extremity. 

 The whole organ is somewhat dilated toward the end, and is furnished with a row of 

 minute spines down the sides of the duct. In the second pair (PL XXV. fig. 7, 8, and 9) 

 the endopodites are each produced into an elongated peduncle, which is deeply grooved 

 on its inner face, and bears a double row of stout, slightly-curved spines near its extremity, 

 and a scoop-like terminal process having smooth edges and with the hollow faces meeting 

 in the middle line. Both pairs evidently act as copulatory organs ; but I have not been 

 able to trace the passage of the vasa deferentia into the first pair, which I think represent 

 the openings of the male generative organs. The second pair appear to act only as 

 clasping-organs. The succeeding 3rd-5th pairs of pleopoda arc similar to the corre- 

 sponding limbs in the females. 



The uropoda form with the telson a large tail-fin (PL XXV. fig. 9), as in most shrimps. 

 In each the basal portion is relatively smaU, while the exopodites and endopodites are 

 produced into large plates or swimmerets ; these are subequal in length, oblong in form, 

 and bluntly pointed : the distal halves of all four plates are densely fringed with long 

 comb-like setaj or spines ; the proximal halves of the inner plates are quite smooth 

 on the outer margin, while those of the outer pltites have a very few short spines. 



The telson is short and almost transversely truncate, its length hardly exceeding the 

 breadth at its base. The blunted end is furnished with a fringe of comb-like teeth. 

 The shortness of this telson is a characteristic feature, as in the majority of Schizopods it 

 exceeds the uropoda in length. It is only in certain genera of Mysidse (e. g. Euchceto77iera) 

 that the latter reach far beyond the end of the telson. The relative width of the uropoda 

 in .4 ??«spV/^6- causes this tail-fin to act as a very powerful swimming-organ, and this 

 enables the animal to retreat very rapidly from any danger menacing it in front. 



The largest specimen of Anaspides examined by me was 38 mm. or 1^ inch long, but 

 the length in smaller specimens hardly exceeds 25 mm. I found ova in the oviducts. 



Anatomical Structure. 



I have met with very considerable difficulty in working out the structure of Anaspides, 

 owing to the imperfect state of preservation of my specimens. These when caught were 

 merely put into alcohol of unknown strength, and even this was not changed for two or 

 three weeks. The result was that all the internal organs were more or less disintegrated. 



