PACKARD.] INTEENAL ANATOMY OF PHYLLOPODA. 401 



however, nucleus-like bodies occur on the points of intersection, I have 

 not yet been able to discover. In the profile view of the animal the 

 central body appears exactly as in the Daphnidce^ in the form of a clear 

 round vesicle in the feeble (matten) brain-substance, and can thus give 

 ready opportunity for illusion. An independent vesicle, such as Glaus 

 describes in Daphnia magna^ I have not seen here. 



"From, the lateral lobes of the suj^racesophageal ganglion arise the 

 following o nerve-pairs : 



"1. The large optic nerve. 



"2. Several nerve-twigs to the eye-muscles. 



"3. A slender fiber on each side to the frontal organ. 



"4. First antennal nerve. 



"5. The ' hirnschenkel.' 



"From the middle division arise only 3 paired and an unpaired 

 nerve, viz : 



" 6. An at least externally unpaired nerve, and 



"7. A i^aired nerve-stem, both to the so-called larval eye. 



"8. An outermost fine fiber on each side, which arises laterally from 

 the seventh pair, and goes above and outside of it. 



"9. A slender pair of nerves to the oesophageal musculature. 



" Of these nerves Zaddach [Apus] knew only those mentioned under 1, 

 4, 5, 7, and 9, but as they occur also in Brancliiims as well as in several 

 Cladocera investigated by me, there can be no doubt that they are pres- 

 ent also in Apus^ and were overlooked by him." 



Spangenberg then describes the ganglion opticum and eye. 



Ventral ganglion chain. — The second cephalic or first ventral iiair of 

 ganglia, which lie on the side of the oesophagus, are the second antennal 

 ganglia. This ganglion, and the 2d antennal nerve which arises from 

 it, is figured by Ellunzinger. • 



Then follows the mandibular and then the maxillary ganglia. These 

 are succeeded by 22 pairs of ganglia. 



There is probably no essential diiference between the nervous system 

 of Estheria and Limnadia. From a number of sections of Estheria mex- 

 icana kindly made for us by Mr. jST. N. Mason, we have drawn figures 

 1, 2, 4, and 5, PL XXXI II, which partly illustrate some points in the 

 structure of the nervous system. Fig. 2 represents a section which evi- 

 dently passed through the brain (br). It is seen to be a double ganglion, 

 with the hemispheres more distinctly marked than in Grube's representa- 

 tion of that ot Limnetis. Fig. 1 and the enlarged view. Fig. 4, passes 

 through a ganglion, which we take to be the brain. The section must 

 have been very oblique, as the oesophagus is seen to appear as if situ- 

 ated above the brain. The section passes througli the larval ocellus, 

 whose cones and ingment mass have still survived, though sunk out of 

 sight under the integument. 



Fig. 5 rei)resents a ganglion posterior to the maxillary ganglion, and 

 probably supplying the nerves to the first pair of feet, and situated 

 directly under the intestine, the epithelium of which is shown in the 

 figure. The histological structure is seen to be very simple. The gang- 

 lion consists of scattered ganglion-cells and fine granules, which may be 

 the ends of fibers, but no distinct fibrous structure was to be detected. 

 The brain, fig. 4 &r, and fig. 2 &r, is apparently no more complex in 

 its histological structure than the ventral ganglia. 



A good deal of time was given to attempts to work out the nature of 



the brain, but though Mr. Mason very kindly made sections of a number 



of specimens of Estheria^ Ajms, and dilierent fresh Branchipodidce, yet 



owing to the inherent diihculties in the nature of the investigation very 



2G H 



