131 



is full and rounded, and which internally is wholly occupied with the 

 nucleogenous bodies or plates, the lobes which we are now to describe 

 residing in the upper half. The nerves to the first pair of appendages do 

 not arise from the base of the brain, but the ganglion cells giving rise 

 to them are situated entirely outside of and behind the brain proper. 



The brain as thus constituted is in the adult made up of three pairs 

 of lobes enveloped by the very thick masses of chromatic cells. The 

 first and uppermost are the pair of lateral-eye lobes. These lobes are 

 situated at the top of the brain , and are widely separated from each 

 other ; the,y are somewhat pyriform , but below contract in size where 

 connected with the cerebral lobes; the lateral-eye nerves are well 

 developed and thick at their origin. The nervous fibrillae (or tubules) 

 appear to originate from the chromatic cells, which do not here form 

 dense masses, but are much scattered, forming a laTge incomplete ring 

 in the interior of the lobe ; these cells have a distinct thin protoplas- 

 mic zone enclosing the nucleus. The lobe just below the middle is 

 seen to be embedded in the dense ring or ruffle-like masses of deeply 

 stained chromatic cells, which, we have called the «nucleogenous 

 bodies « . 



After passing in horizontal sections through the lateral- eye ner- 

 ves, the knife cuts through the origin of the median-eye nerve and the 

 lobes from which they originate. These lobes are in the adult brain situa- 

 ted far below the plane of the lateral-eye lobes , and they are difficult 

 to detect, owing to the fact that they are small and slender and not 

 much swollen or spherical. They form two narrow tracts of myeloid 

 or punctured substance arising near the middle of the brain from the 

 inner aspect of the cerebral lobes, their roots or base being situated not 

 far from the cerebral commissure. Their lack of a definite pyriform 

 shape and their small size indicate that they have probably somewhat 

 atrophied. The nucleogenous bodies are closely packed around the 

 origin of the nerves. There is below the median-eye lobes a pair of 

 minute lobes, each sending off a bundle of fibrillae backward towards 

 the cerebral commissure which may possibly give rise to a pair of te- 

 gumental or »haemal« nerves. I have been unable as yet to detect any 

 traces of lobes or nerves belonging to Patten's »median eye of the first 

 segment 4 «. 



The third pair of lobes are the cerebral lobes. These are very irreg- 

 ular in outline, slender, and apparently shrunken, and very different 



4 Patten considers that a diverticulum of the median eye-bulb »represents in all 

 probability, a pair of eyes belonging to the first brain-segment« and that conse- 

 quently there are »three fused ocelli« in Limulus. On the origin of Vertebrates from 

 Arachnids. Q. Journ. Micr. Sci. XXXI. 344. 1890. 



