362 ARTHROPODA 



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

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

 bases of the maxillae (fig. 383, s). The green gland opens similarly on the 

 bases of the second antenrue. Both have essentially the same structure 

 (fig. 377) ; they begin with a terminal vesicle, which passes into a slender, 

 greatly coiled tube. Both occur together only in the larva?; in the adult 

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

 diverticula developed from the intestine (fig. 409), which resemble the 

 Malpighian tubes of insects, but differ from them in being of entodermal 

 origin. In some decapods caeca 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 and consisting of an X-shaped pigment mass in which are placed 

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

 are distinct from ocelli, but recall the eyes of Platodes. Both kinds of 

 eyes may coexist in the same species. 



Auditory (equilibration) organs (otocysts) occur only in the Malacos- 

 traca, either in the base of the first antennae or (Schizopoda) in the en- 

 dopodite of the last abdominal feet (fig. 396, o) with a large statolith 

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

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

 with a row of chitinous sense hairs, the crista aciistica, connected below 

 with an auditory nerve, while their free ends extend between a cluster of 

 statoliths. 



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

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

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

 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 statocysts, but apparently they are 

 also auditory, since some forms which have well developed otocysts have no 

 statoliths. 



Crustacea are only exceptionally hermaphroditic. The spermatozoa are 

 noticeable for their great size, in many ostracodes equalling the body in length 

 (Pontocypris paradoxa, 8 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. 

 37, III, IV). They are frequently enclosed in spermatophores (fig. 385). 



The typical development of a crustacean includes a metamorphosis, 

 and where direct development occurs the metamorphosis is either sup- 

 pressed or the corresponding stages are passed in the 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 



