200 PATTEN AND REDENBAUGH. 



EXPLANATION OF PLATE X. 



Fig. 9. A portion of the cardiac plexus of Fig. 8 enlarged 40 diameters. 



The masses of ganglion cells (^g-c.) m. the median nerve (m.c.n.) are more dis- 

 tinct, and the courses of the individual fibers in the plexus and lateral nerve {l.c.n.) 

 are more apparent. Two of the ostia {osJ ''"'^ ^) are represented. 



Fig. id. A small portion of the median cardiac nerve {m.c.n.), enlarged 500 times. 



The individual nerve fibers and the ganglion cells {g-c), with their processes, 

 are easily made out. 



Figs, xi and 12. The brain of Limulus from the neural and haemal sides, 

 respectively (enlarged about 3 diameters). 



The enveloping arterial sheath has not been removed. The anterior commis- 

 sure {a.c.) with the three rostral nerves {l.a.n.) is seen in Fig. 11, behind the fore- 

 brain {f.br.'), and four of the post-oral commissures {p.o.c.^'^) can be made out 

 posterior to the central canal through which the oesophagus passes. The first 

 post-oral commissure {p.o.c.^) is separated from the others, and is much longer as 

 it passes haemal to the oesophagus. 



Three olfactory nerves (o/.n.) arise from the anterior side of the fore-brain, and 

 a median eye nerve (tn.ey.n^ comes through the arterial sheath a little to one side 

 of the median line and near the haemal surface. From the haemal side of the 

 fore-brain arise the two large lateral eye nerves (l.e.n.) with ganglionated bases 

 (Fig. 12). 



Just back of the fore-brain upon the neural side, the cheliceral nerves («.«.', 

 Fig. 1 1) arise and give off, near their bases, from one to three small nerves to the 

 tergo-coxal muscles of the chelicerae. 



Five more pairs of large neural nerves («.«.-"*) radiate from the circum- 

 oesophageal collar to the next five pairs of thoracic appendages. Each of these 

 gives off on the neural side a mandibular branch {m.n.^'^) and upon the haemal 

 side several ento-coxal nerves. The typical numbef of ento-coxal nerves is three ; 

 an anterior {a.e.n.^), a posterior (f.e.n.^), and a median [m.e.7t.^) ento-coxal nerve. 

 From the second haemal nerve [h.n.'^) four ento-coxal branches are given off, in 

 some cases ; but two of these may be regarded as branches of the anterior and 

 posterior ento-coxal nerves; the median ento-coxal nerve has not been found. In 

 the case of the sixth neural nerve («.«.*) the median ento-coxal nerve (m.e.n.^) is 

 much enlarged and becomes the flabellar nerve. 



The chilarial (n.ti.'^) and opercular nerves {n.n.^) are much smaller than the 

 other neural nerves, and arise from the posterior side of the brain (Fig. 11) 

 neural to the ventral cord {v.c). 



From the haemal side of the brain (Fig. 12) the delicate lateral nerves (/.«.), or 

 first pair of haemal nerves, arise just back of the lateral eye nerves {l.e.n.). 



The next seven pairs of haemal nerves (//.«.^"^) radiate from the circum- 

 oesophageal collar. Of these the anterior pair {h.n.'^) are somewhat larger than 

 the others and give off close to the brain a small nerve (i.n.^) which innervates 

 the tergo-proplastral muscles. 



The posterior three pairs (/i.n.^'^) give off intestinal nerves (/.«.*'^), two of 

 which («'.«.* 3"'^ 7) go through foramina in the endocranium. 



A pair of stomodaeal nerves (si.n.) arise from small ganglia upon the inner 

 side of the circum-oesophageal collar. Sometimes small nerves are given off to 

 the oesophagus from the stomodaeal ganglia. 



