430 si'M^rARV OF rrnnr.NT HESE.vnrHKS urlatixo to 



pigments or mollifications of the snmo jjii^moiit, which tire widely 

 distributed in tlie animal kingdom, and to which myoha-matin belongs. 

 The liistoha?matins are respiratory pigments, as can bo proved by 

 oxidizing and reducing them in the solid organs. Their bands 

 ocenpy almost the same jilace as those of myohajniatin. In the 

 snin'arcnals of man, cat, and some other animals, the medulla gives 

 the spoctruiM of hremochromogen, while the cortex shows that of 

 histohaGmatin. Hfomochromogen in a vertebrate body is probably 

 excretory and must be so regarded here, hence tlie function of the 

 adrenals must be (at least in part) to metamorpliose effete luumoglobin 

 or hannatin into haemocliromogen. An active metabolic process takes 

 place in the adrenuls, and the author concludes that they have a large 

 share in the downward metamorphosis of effete colouring matter, and 

 that these observations will htl]) to throw some light on Addison's 

 disease. 



Homologies of the Vertebrate Crystalline Lens.* — Dr. B. Sharp 

 traces the stages of the development of the eye from the simple 

 deposit of pigment in an epithelial cell to the highest form, that of 

 the Vertebrata. 



The successive steps are as follows : — The first visual organ 

 primarily consisted of a deposit of pigment, centralized at the oral 

 pole. The next steji is the formation of invaginated grooves, which 

 gradually form a sphere and protect the organ. The refracting 

 media of separate cells soon coalesce, to produce a cuticular lens. 

 The nerves of general sensibility become specialized and form a distinct 

 (primitive) optic nerve ; corresponding stimulation takes place in the 

 brain. Increased activity causes increased development all along the 

 tract from the eye to the seat of vision in the brain. That part of 

 the brain nearest to the eye eidarges, and proceeds by steps toward 

 the eye, the primitive optic nerve still connecting the two. In the 

 next stage, part of the brain closes over the superior part of the eye, 

 being se2)arated by a layer of fibres, which is the much shortened and 

 flattened primitive optic nerve. The pedicle connecting this ad- 

 vanced part of the brain may be looked upon as a ganglion and soon 

 becomes the most important part of the eye and receives the light- 

 waves upon its exterior wall, the primitive eye becoming transparent 

 and later forming the lens. This ganf/lion opticum, as it may be 

 provisionally called, gradually proceeds downwards about the primi- 

 tive eye, joining below. As development advances the ganglion is 

 hollowed out and later is filled with the corjms vitremu, which is 

 included in it. 



Thus the lens of the Vertebrata is homologous with a primitive 

 invaginated eye, such as we find to-day in the Gastropoda ; the layer 

 of optic fibres of the retina is homologous with the primitive optic 

 nerve. As the retina below has become the sensory part of the eye, 

 the rays must necessarily pass through it to reach a point where 

 nerve-energy is developed. The nerviis opticus of the eyes of the 

 Vertebrata is, therefore, really a secondary optic nerve. 



♦ Proc. Acad. Nat. Sci. Philad., 1884, pp. 300-10 (4 figs.). 



