NOTES ON THE EMBRYOLOGY OF LIMULUS. 
553 
ally fuse with the “ brain. 5 ’ In Limulus the same process 
occurs but stops just short of the fusion of the corresponding 
ganglia with the pre-oral ones. For a knowledge of the condi- 
tion of the brain in the Scorpions, one must await a detailed 
account of the structure. As the case is at present Dr. 
Packard distinctly states ( 5 80 a ) that the brain supplies the first 
pair of appendages ; while Newport’s figure (’ 43 , pi. xii, fig. 15) 
shows the nerves as arising from the side of the brain. Newport 
was a very careful worker but the subject needs further study. 
On the other hand, in all the Crustacea, not excepting Apus and 
Limnetis (Branchiopoda), this coalescence of ganglia has gone 
still further than in Limulus or Arachnids, and even in the 
earliest stages the first pair of appendages are pre-oral in inner- 
vation, while the ganglia of the second pair (Apus excepted) 
move forward with growth from a primitively post-oral position 
and form an important part of the brain. 
Fourth in the series comes the presence of simple lateral 
eyes in the Arachnids and compound eyes in the other. I 
have not yet studied my sections of the eyes of the young 
carefully enough to throw any light on the question. Since 
Dr. Packard wrote, Lankester and Bourne have shown (’ 83 ) 
that if a comparison be made of the whole compound eye 
of Limulus with the entire lateral group of the Scorpion 
the correspondence is very nearly perfect ; and that “ if we 
supposed a common ancestor of the Scorpion and King Crab 
to have exhibited a lateral ‘ ocular area ’ which possessed 
a single feebly developed cuticular lens, then by two slightly 
divergent lines of differentiation we can obtain the grouped 
eyes of Scorpio on the one hand, and the polymeniscous 
eye of Limulus on the other hand.” The same authors 
also show that “ the essential agreement of the central eyes 
of Limulus with those of Scorpions is obvious.” As to Pro- 
fessor Lankester’s well-known accuracy in histological work 
no comment is necessary and no confirmation is needed, but I 
would say that before his results were published I carefully 
studied the eyes of the adult Limulus, and so far as that 
