444 DR. J. F. GBMMILL OK [Apr. 10, 



may best be taken as the basis of classification, and my specimens 

 belong to two types. The first is chai'acterised by fusion, more or 

 less complete, of the cerebral lobes (one specimen) ; the second by 

 fusion of certain structures in the mid-brain as well as of the 

 cerebral lobes. 



(A) Cydo'pia tvlth Ftosion of the Cerebral Lobes {one specimen). 



The external appearance of this specimen is illustrated by 

 PI. XXXII. fig. 1. The front of the head is wedge-shaped, its 

 size being reduced in the tiunsverse and increased in the vertical 

 line. The large median eye is overarched by a mesial frontal 

 process carrying a pair of small closely approximated olfactory 

 pits (fig. 2). Upper and lower jaw arches are present. The 

 posteiior part of the head and the body are normal. 



Cranial /Skeleton. — The skeleton is greatly modified in front of 

 the pituitary region. The trabecules cranii pass downwards so as 

 to lie below the median eye (fig. 4). They are widely separated 

 fi'om the base of the brain and they take no pai't in the formation 

 of an olfactory capsular cartilage. Anteiiorly they articulate 

 with short palato- quadrate bars. In the normal Trout embryo at 

 a corresponding stage the trabeculfe, though united, still show 

 evidence of their double origin. But in all my cyclopean specimens 

 the trabecuke form an absolutely single piece right back to the 

 pituitary space. 



A rudimentary olfactory capsule is derived from the united 

 anterior ends of the supra-orbital bars. This vinited portion lies 

 in the frontal pi'ocess and is perforated by the two small olfactoiy 

 nerves. Posteriorly the supra-orbital bars separate and pass 

 along the dorso-lateral aspects of the brain to join the auditory 

 cartilages, as in the noi'mal condition. Near their place of 

 separation each gives origin to an obliquus oculi superior muscle. 



The mandibular, hyoid, and palato-quadrate bars are appreciably 

 shortened in accordance with the small transverse measurement 

 of the mouth. 



Brain. — The cerebral lobes are slightly smaller than normal, 

 and are in great part united along the inner faces. The longi- 

 tudinal fissure penetrates for only a third of their depth in front 

 at the place of origin of the olfactory nerves, while posteiiorly 

 close to the third ventricle the fissure in question appears simply 

 as a shallow groove (fig. 3). The third ventricle and the optic 

 lobe regions are well developed, pineal diverticula, optic recess, 

 hypophysis, and hypoaria being present as in the normal condition. 

 There is no dropsy of the central cavity of the brain or of the 

 meninges. The cranial nerves are all present and are normal, 

 with the exception of the first two pairs, the olfactories being 

 small and closely approximated, while the optic tracts unite at the 

 chiasma to form a single optic nerve. 



Eye. — The globe is large and has its transverse diameter 



