630 RECOBD OF CURRENT RESEARCHES RELATING TO 



the supra-oesoiihageal gauglion is one of a tergal series of ganglia cor- 

 respontling to the more fully developed sternal set, and so the I'egion 

 itself may consist simply of terga whose development has been affected 

 by the disproi^ortionate growth of the terga posterior to them, which 

 constitute the carapace. 



Shortened Development in Palaemon potiuna.* — To the list of land 

 and fresh-water animals which dispense with the development through 

 which their marine allies pass, Dr. Fritz Miiller adds the Brazilian 

 Trichodactylns and ^glea Odebrechtii from the Decapod Crustacea. The 

 fresh-water shrimps of the mouth of the Itajahy, however — a Leander, 

 a Pcdcemon, and a species of the Atijince — leave the egg in the zooea 

 stage. On the other hand, the female of Palcemon potiuna, instead of 

 laying the large number of eggs usual with kindred species under the 

 same conditions, produces from six to twenty large ova, 2 mm. in 

 length, from which issue young of 5 mm. length, having all the deport- 

 ment of adults, whose form they assume fully at the fourth change of 

 skin. The condition in which the young leave the egg is that of the 

 larva of Hipiiolyte polaris, except that the gills arc well developed 

 while the mouth-parts are mere rudiments. 



The changes through which the different organs pass with the four 

 changes of skin are as follows : — 



Frontal process of the carapace, from a short tooth- and hairless 

 process to one with generally six to seven teeth, with corresponding 

 tufts of hair in front of them on the upper edge and one or two on the 

 lower edge, which bears a double row of hairs. 



Front edge of carapace at first bears a single inferior bristle, and 

 finally an antennal and hepatic bristle, a branchiostegal having 

 appeared in the fourth stage, and having apj)arently fused with the 

 hej)atic in the last stage. 



Front antenna at first zooeiform ; protopodite unsegmentcd, a 

 bristle on the inner branch, two such on the outer one ; finally, each 

 of the last segments (generally ten in the male) of the inner division 

 of the outer branch bears two transverse series of two or three olfac- 

 tory filaments each. 



Hind antenna, from having only the outer branch segmented, has 

 both segmented, and provided, the one with bristles, the other with 

 numerous bristles and a spine ; this condition is reached at the second 

 stage. 



Mandible becomes two-branched, toothed, with a palp, instead of 

 consisting of a single simple cylinder. 



Maxillce do not alter, nor do the anterior maxillipedes, materially. 



Middle and posterior maxillipedes : the inner branches from the 

 beginning are long, strong, and devoid of swimming hairs, but carry 

 terminal claws, serving as legs ; the only change is that they become 

 comparatively weaker. 



Chelate feet, from a segmented but rounded, hairless, immobile 

 form to chelate appendages with comb-like ornatory spines (the pos- 

 terior pair becomes longer than the body in very old males). 



* ' Zool. Anzeig.,' iii. (1880) p. 152. 



