47 



PLATE XXTTI. 



THE FROG— contmued. 



Development — 



Fig. 1. Eggs, natural size (see PI. XXII. fig. 12, Egg magnified)— 

 a. Ovarian ova. 



6. Laid eggs, siu'vounded by successive layers of albumen or wliite of egg secreted by the oviduct 

 and swelling up in water. 

 Fig. 2. Impregnated Egg showing successive stages in the process of yelk-division — 



Tlie immediate result of this process is the formation of a morula (/), which by the soaking in 

 of fluid into its interior becomes a hollow sphere. 

 DiAG. 1. Development of Tadpole — 



r Outer layer or epiblast. 

 a. Blastoderm or germinal membrane < Middle layer or mesoblast. 



V Inner layer or hypoblast (blue). 

 JleduUary groove, a median longitudinal depression. 

 Laminse dorsales (L. dorsal plates) or medullary folds, the epiblast raised up into folds on 



• each side of medullary groove. 

 Xotochord or chorda dorsalis, the primitive axial column. 

 d. Neural canal formed by the union of the dorsal lamin;e, with neural archer in its walls. 

 Centra of spinal column invest notochord, which persists both in the centres of the bodies 

 of the vertebrae and in the urostyle. 

 /. Spirally-coiled intestine. 

 Large muscular tail. 



Chief phases in life of Tadpole shown in PL XXII. 

 Fig. 3. Perfect Frog, tailless, in natural position. 

 Classification — 



Sub-Kinqdom — Vertebrata, because it possesses a vertebral column ; limbs with an internal 



skeleton ; and a portal vein with a capillary network at both its ends, receiving the 



capillaries of the alimentary canal, and distributing to the capillaries of the liver. 



Class — Amphibia (Gr. amphi, both; bios, life), because as a Tadpole it has gills, afterwards 



lungs ; two condyles on the skull for articulation with the vertebral column ; and a cloaca. 



Natural Order — Anou'ra (Gr. a, without ; oura, a tail), because devoid of tail and gills in 



adult life. 

 Genus — Kana. 

 Common Name — Frog. 



Comparative Histology of Frog and Man. 



Figs. 4, 4a. Blood-Corpuscles — 



f Frog — large, oval, and nucleated. 

 \ Human — smaller, round, and non-nucleated. 

 Colourless, like amoebae (see PI. IX. tig. 4). 

 Figs. 5, 5a. Epithelium (Gr. epi, upon ; thallo, I grow) in its principal varieties— 

 a. Squamous (L. squama, a scale) or scaly. 

 h. Columnar or cylindrical. 

 c. Ciliated. 



Spheroidal or glandular (see PI. XXIL fig. II). 

 Fig. G. a, h, c. Connective Tissue in its two principal varieties- 



( Connective-tissue corpuscles, nucleated cells. 

 White Fibeous Tis.sue ■' ^ . • «, 



( Matrix, fibrous. 



YELL0^\■ Elastic Tissue, resisting acetic acid. 

 Fig. 7 and Diag. 2. Vertical Section of Epidermis or Epithelium. 

 Fig. 8. a, b. Cartilage or Gristle — 



( Matri.x, granular. 



Cartilage -^ Cartikgfr cells, nucleated. 



