384 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



spindle-shaped ganglion-cells before terminating in the spherical gan- 

 glion-cells at the insertion of the three setse. The same general ar- 

 rangement of the nerve-fibers and cells is seen in the same organs earlier 

 in life at fig. 3. 



In Chirocephalus Jiolmani, according to Dr. Gissler's figure, the first an- 

 tennae each bear not only three terminal setse, but also a series of about 

 five sense-setse like a ten-pin (Fig. 8). These are apparently homologous 

 with the olfactory cylinders of Leydig* on the smaller antennae of Asel- 

 lus aquaticus. 



The second antenncc. — These are not apparently organs of any special 

 sense. In the Limnadiadce they are evidently derived from the "ruder- 

 arme " of the Oladocera, being large, long, biramous appendages of con- 

 stant use as oars in swimming, the long setae assisting in the oar-like 

 movements. The form is very persistent in this family, the use of the 

 appendages being the same in each genus. 



In the BrancJiipodidce, the second antennae of the males are modified 

 in a striking way, which afford apparently good specific characters useful 

 in such a difficult genus as StreptocephaUcs. As clasping organs their 

 use is seen in the engraving of Artemia (fig. 17 in text). The rounded 

 sinus between their bases just fit over so as to inclose the back of 

 the female, and the two knob-like processes further seem to hold her 

 fast; in Branchinecta the structure of the base of the claspers is the 

 same, while the simple unarmed second joint is not particularly well fitted 

 for prehension. In Branchipus each second joint has a stout spine 

 pointing inward which acts as a prehensile apparatus, as has Streptoce- 

 phalus, in which also the second joint is variously divided into prehensile 

 parts. 



In Chirocephalus and Thamnocephalus the second joint is incurved, 

 and thus rendered sufficiently j)rehensile. 



It appears, then, that the highly specialized male second antennae 

 have lost perhaps altogether their sensory functions, or their use as 

 swimming organs, like those of the LimnadiadcB^ and are simr)ly of use 

 as clasping organs and minister solely to the reproductive function. 



In the Apodidce^ as stated by Lankester (Quart. Jour. Micr. Sc, April 

 1881, p. 346), the existence of the second pair of antennae has recently 

 been denied. "Zaddach states that they were generally absent in A. 

 cancriformis, but were found by him in two'cases; Huxley states that 

 he was unable to find them in Apus glacialis examined by him, whilst 

 Glaus, whose statements have the very greatest weight, both on account 

 of his extended investigation of the morphology of the Crustacea and of 

 his special observations on the development oi^ Apus and Branchipus, 

 brings forward the total absence of the second pair of praeoral append- 

 ages in Apus, as a special characteristic of the family Apusidae." Gers- 

 taecker simply, in reference to this point, quotes Zaddach's statement. 

 Lankester adds "In the adult Apus cancriformis and Apus dulcii, from 

 Affghanistan (?A. himalayanus), this second pair of j)rasoral append- 

 ages, although reduced to a rudimentary condition, is always present, 



* Leydig, F. Ueber Geruchs- unci Gebororgan der Krobse und Insecten. Reichert u. 

 du Bois-Raymond's Archiv. 1860, Tab, 7, fig. 4. 



Spangenberg (on Limnadia hermanni, Zeits. fiir W. Zoologie Suppl. 1878) tbus de- 

 scribes the taste-organs. On the 1st antennae "they arc situated — usually six in num- 

 ber — as small, clear points on the hinder nuich-swoUeu surface of the base of the an- 

 tennae, and may be traced back, as all these taste-filaments, to the spines on the nau- 

 plius-antennae. The structures on the base of the known pale taste-cylinder, described 

 by Clans as 'highly characteristic shaped nerve-pins,' are the young taste-cylinders, 

 reaching out in the succeeding moult, and are not of a nervous nature, but cuticular 

 early growths." 



