CENTRAL NERVOUS SYSTEM IN PLANARIA. 5! 



diately into two nerves passing to the front of the head (Fig. 24). 

 In Fig. 25 it becomes evident that the apparently single eye is 

 actually double. One of the pigment cups lies slightly anterior 

 and \i-ntral to the other and somewhat to the left of it. The 

 opening <>f the more posterior and dorsal cup i- -een in Fig. 25, 

 while tli- other pigment cup appears here as a complete circle. 

 P.oth open antero-ventrally and toward the right. The gan- 

 Jionic ma i- not divided into right and left halves and the 

 optic nerve- arise from its median region. Both eyes are far 

 belo\\ i he dor-al surface of the body and the more ventral one 

 i- imbedded in the- ganglion. 



The double nature of the eye is not apparent in the living 

 animal since the two pigment cups lie so close together and one 

 i- almo-i \entral to the other. 



l'< -icrior to the level of the eyes the ganglion i- abnormal in 

 lorm to about the posterior end of the regenerated region. I 

 Jo. .1 -e< lion -li-htly anterior to the boundary bet \\een ne\\ and 

 old tissue, shous that in general form and arrangement of the 

 hi MI ILK i- i he ganglion at this level resembles that of Case i 

 Fig. 13). \ little farther posteriorly, in the old tissue, it 

 di\ide- into lijn and left j>ortions and gives rise to t\\o nerve 

 cords ot tin- n-nal form, but somewhat nearer together in their 

 anteHo] region than in normal forms. 



.V Tin- case is like Case 4 in external appearam < IK 23 

 and al-o in the number and arrangement of the eyes, but -onie 

 diltereine- in the structure of the nervous system e\i-t. I ig. 28 

 -hou- the le\ el of origin of nerves to the front of the head, a l<-\ el 

 -liJnK anterior to the eyes. In Fig. 29 the eyes an seen to be 

 ^lightly larger than in the preceding case, but other\\i-e -imilar 

 to it. Hoth open antero-ventrally and toward the ri^hi and one 

 lie- to the K It of, \-entral and slightly anterior to the other. The 

 gan^lionie ma-- is single, but larger than in ( a-e 4 at tin- level 

 I igs Jo and 25 and the optic nerves ari-e Irom it -omeuhat 

 to the ii-ht of the middle. 



Posterior to the eyes the ganglion -ooii -lm\\ - di-tinct right 

 and left hal\e- but these are abnormal in -hape and each is 

 broki'ti iij) into a number of more or le-- di-tinct liber trai 

 \\hich. however, are apparently symmetrically ariMtt^ed in the 



