400 GEOLOGICAL SUEVEY OF THE TEREITOKIES, 



endite has its distinct blood passage, and thus respiration takes place 

 all tb rough the appendage. 



The nervous system. — The nervous system is quite uniform in the Phyl- 

 lopods, and that of Limnetis has been described by Grube, that of Lim- 

 nadia by Klunzinger,* and more lately by Spangenberg, and that of 

 Apus by Zaddach, while the brain and nervous cord of the young 

 Branchipns stagnalis has been figured and described by Clans. 



Oar Plate XXXI, fig. 8, copied from Grube's drawings, illustrates the 

 nature of the brain and nervous cord of the European Limnetis brachyura. 

 The brain is very small, forming a single flattened mass from which the 

 large optic nerves arise. The first antennal nerves arise from the begin- 

 ning of the commissure, which forms an oesophageal ring, and the second 

 antennal nerve arises opposite the transverse commissure, which com 

 pletes the oesophageal ring behind. Then succeed the i)eculiar ladder-like 

 ganglionated ventral cord ; from the two anterior ganglia arise respect- 

 ively the mandibular and maxillary nerves, the third pair of ganglia 

 supplying the first boenopods. 



The anatomy of the nervous system of Limnadia hermanni has been 

 fully described by Spangenberg,! but unfortunately he has given no 

 illustrations. The following account is translated from his paper: 



" The nervous system of Limnadia shows the greatest agreement with 

 that of Apus. It has a primitive, embryonal character, as that of Apu^. 

 This is seen in the ganglions of the second antennse. These are in most 

 Crustacea united in a common mass with the brain. In Limnadia not 

 only the ganglion-swelling, but also the two transverse commissures 

 uniting them preserve their original form, and the ganglion pair of the 

 second segment differ here in no important point from that of the other 

 segments, except in the lip-commissure springing from it. There also 

 remain the ganglia of the ventral cord in the last body segment, both 

 longitudinally and transversely well separated from each other, while 

 in Branchipns and Artemia they are not more perfected, but in Apus 

 sutler a widespread consolidation. 



"The central nervous system of Limnadia consists, as that of all Phyl- 

 lopods,of a two-lobed supraoesophageal ganglion before the oesophagus — 

 scarcely properly called a brain — and right behind the oesophagus, be- 

 tween the digestive canal and floor of the body a ladder-like ventral 

 chain of 2G ganglia, the tail segment being without a ganglion. 



'^ Brain. — The supraoesophageal ganglion consists of two spindle- 

 shaped lateral lobes and one unpaired median section. All these pos- 

 sess their own centers and send out the nerves originating from them. 

 Such centers are five in all, four arranged in pairs in the lateral loljes, 

 the fifth unpaired in the middle lobe. 



"Of the two paired centers the foremost is by far the largest ; it serves 

 as the central organ for the optic nerve, the eye-muscle nerves, and 

 furnishes the nervous tract reaching to the so-called larval eye. The 

 smaller, situated somewhat farther behind, lying under and external, 

 sends fibers to the first antennal nerve. What significance the bean- 

 shaped central body of the middle lobe, met with in all Phyllopods, has is 

 not clear to me. It lies perpendicular to the longer axis of the animal in 

 the hinder third of the middle lobe between the commissural threads 

 passing from one lateral lobe to the other. From all sides pass curved 

 nerve-fibers into it, which are variously covered and intertangled with 

 one another. It consists quite unlike the paired centers of large 

 ganglion-cells, but solely of the so-called Leydig's punctsubstanz.i a con- 

 fused mass of the finest fibers variously matted together. Whether, 



* See his figure in Sieb. u. Koll. Zeits. w. Zool. XIV, Taf, XIX, fig. 26. 

 t Zeitschrit't fiir wissenscli. Zoologie. Supp. 1878. 



