. The biology of the frog . igment, bothyellow and black. The pigmented cells have the propertyof absorbing pigment granules with which they come incontact; if coloring matters are injected into the blood, theyare taken up by these cells in large quantities (Ponfick,Siebel). The spleen also contains large cells in which redblood corpuscles are frequently found in all stages of degen-eration. The spleen is an organ having various functions. It is aplace where red blood corpuscles are destroyed, probablywhen they have reached a moribund condition. Pigmentand other foreign matters in the blood ar
. The biology of the frog . igment, bothyellow and black. The pigmented cells have the propertyof absorbing pigment granules with which they come incontact; if coloring matters are injected into the blood, theyare taken up by these cells in large quantities (Ponfick,Siebel). The spleen also contains large cells in which redblood corpuscles are frequently found in all stages of degen-eration. The spleen is an organ having various functions. It is aplace where red blood corpuscles are destroyed, probablywhen they have reached a moribund condition. Pigmentand other foreign matters in the blood are taken up bycertain cells of the pulp. Leucocytes are in all probabilityformed in the spleen, as various stages in their productionhave been observed, and it has been found that there is agreater number of these cells in the blood of the splenic veinthan in that of the splenic artery. According to some investigators the spleen produces aninternal secretion which acts upon the pancreas so as to THE BIOLOGY OF THE FROG ,-*. R Fig. 60. — Diagram show-ing the position of thethyroid glands, t; /,lateral process of hyoidcartilage; , thyro-hyoid process of hyoid. tion in Rana pipiens. convert the proteid-splitting enzyme of that organ into an active form. Doubt has, however, been recently thrown uponthis conclusion. The Thyroid Glands. —The thy-roid glands of the frog are com-pletely separated from each other,being situated on either side of thehyoid apparatus in a small spacebetween its posterior lateral andthyro-hyoid processes. Gaupp hasdescribed some thyroid tissue (ac-cessory thyroid) on the ventral sideof the hyoglossus muscle, and I havebeen able to confirm this observa-The tissue of the thyroid shows a unique structure, being composed of a mass of rounded follicles united by a small amount of con- nective tissue in which there is a rich supply of blood ves-sels. Each follicle is a perfectly closed sac lined by a sin-gle layer of cubical epithelial cells. In the
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