362 ARTHROPODA 



(antennal glands") and sJicll glands. The latter (so called from the erroneous 

 idea that ihey produced the shell) open to the exterior on either side at the 

 bases of the niaxilkt? (lig. 3S3, s). The green gland opens similarly on the 

 bases of tlie second antenn;e. Both have essentially the same structure 

 (fig. 377); tliey liegin with a terminal \'esicle, wlrich passes iiito a slender, 

 greatly coiled tulie. Both occur together only in the larv;e; in tlie adult 

 one or the other is suppressed. In some amphijiods there are excretory 

 diverticula de\eloped from the intestine (lig. 400), wliich resemble the 

 INIalpigliian tulles of insects, but differ from them in being of entodermal 

 origin. In some decapods c;i?ca occur in the same region, but nothing is 

 known of their function. 



Besides compound eyes there may be a 'nauplius eye' situated on the 

 brain aird consisting of an X-shaped pigment mass in wliich are placed 

 three lens-formed groups of visual cells, connected with nerves. These 

 are distinct from ocelli, l.ait recall the eyes of Tlatodes. Both kinds of 

 eyes may coexist in the same species. 



Auditory (eipiililiration) organs (otocvsts) occur oitlv iit the jNfalacos- 

 traca, either in the liase of the hrst anteirna^ or (Scliizopoda) in the eir- 

 dopoiUte of the last abdominal feet (lig. 396, 0) with a large statolith 

 of calcium fluoride. The antennal ears of Decapoda (tig. 378) are sacs, 

 the opening to the exterior protected by strong hairs, and eacli internally 

 ■\^-ith a row of cliitinous sense hairs, the crisia acaslica, connected below 

 with an auditory nerve, wliile their free ends e.xtend between a cluster of 

 statoliths. 



At ecdysis these otocvsts with their sensory hairs and statoliths are cast off. 

 If a crayfish which has just molted be placed in perfectly clean water, the otocvst 

 will remain without statoliths; but if some easily recognizable substance, Hke 

 uric acid crystals, be placed in the water, some of these will soon be found in 

 the sac, thus proving; that the statoliths are introduced from the outside. 

 Experiment shows that these organs are stalocvsls, but a|ii)arenllv thev are 

 also auditory, since some forms which ha\e well ilex'cloped otocvsts have no 

 statoliths. 



Crustacea are only exceptionallv hermaphrodilic. The spermatozoa are 

 noticeable for their great size, in many oslracodes equalling the bodv in length 

 {Ponlocypris paradoxa, S times as long as the body — 5-7 mm.). Except in the 

 Cirripedia the spermatozoa lack a flagellum and (Ostracods excepted) are 

 immobile. Their round or elongate body is covered with rigid processes (fig. 

 3 7, III, I^')• They are frequently enclosed in spermatophores (fig. 3S5). 



The typical devclopmeitt of a crustacean includes a metamorphosis, 

 and where tUrect development occurs the metamorphosis is either sup- 

 pressed or the corresponding stages are passed in Ure egg. Two of the 

 larval stages are especially important, the nauplius and the zoea. The 

 nauplius (figs. 7, 393) consists of three segments covered by a dorsal 



