TURTOX NEWS 



Shark. The basal cells of the epidermis 

 are cuboidal; the intermediate region con- 

 sists of irregular angular cells, of a 

 typical prickle cell nature; on the surface 

 is a single layer of much flattened cells. 

 Directly under the epidermis is a layer of 

 loose fibrous tissue, supplied with capil- 

 laries, and under this a thick layer of 

 dense white fibrous tissue. There are two 

 kinds of pigment cells, one group located 

 just under the epidermis and the other 

 group deep in the dermis. The epidermis 

 contains many simple, sac-like glands, 

 each lined with a layer of flat cells and 

 opening to the surface. The secretion 

 seems to be mucous, but this could not be 

 definitely determined from the sections 

 studied. 



Placoid scales are the most interesting 

 structures in the shark skin, because of 

 their similarity to mammalian teeth. The 

 scale is made up of secretions from the 

 epidermis (ectoderm) and dermis (meso- 

 derm). On its external surface is a layer 

 of very dense limy secretion produced by 

 a group of modified epidermal cells. The 

 base of the scale spreads and is rooted 

 deeply in the dermis, which has produced 

 this portion of the scale. Its inner surface 

 (the pulp cavity) and the basal portion of 

 its outer surface are clothed with osteo- 

 blasts. The pulp cavity contains loose 

 fibrous tissue and blood vessels. 



Perch. Here we find the most typical 

 stratified squamous epithelium so far en- 

 countered. The basal cells are columnar, 

 and there is a regular progression toward 

 the surface, each cell being thinner than 

 the preceding one, until on the surface 

 we find several layers of typical squamous 

 cells. Between and on the under surfaces 

 of the scales the epithelium is reduced 

 to a very thin layer of flattened cells. 

 The dermis consists of a thick layer of 

 dense white fibrous tissue and under it a 

 thin layer of loose areolar tissue. Pig- 

 ment cells are found on the inner surface 

 of the dense fibrous tissue and others in 

 the thin layer of fibrous tissue covering 

 the scales. The epidermis contains many 

 unicellular mucous glands. The scales are 

 entirely mesodermal, being completely 

 surrounded by fibrous tissue. Each scale 

 has an actively growing region near its 

 free edge, with osteoblasts and capillaries 

 in evidence. 



Frog. The epidermis is typical strati- 

 fied squamous epithelium, the cells rang- 

 ing from columnar in the basal layer to 

 squamous on the surface. Directly under 



the epidermis there is a layer of loose 

 fibrous tissue with many lymph spaces 

 and glands. Below this the dermis proper 

 is a dense fibrous tissue. On its lower 

 surface there is an abundance of blood 

 vessels and lymph spaces. Pigment is of 

 two kinds; the epidermal cells contain 

 pigment granules, thicker in some places 

 than in others, while an occasional chroma- 

 tophore is found among epithelial cells. 

 In the sub-epidermal connective tissue 

 are found large numbers of chromato- 

 phores, which are much branched. Glands 

 are sac-like, and located in the surface 

 layers of the dermis, with openings to 

 the surface of the skin. The most numer- 

 ous are mucous glands, lined with a 

 cuboidal epithelium and opening by short 

 ducts. Less numerous, much larger and 

 grouped on specific parts of the skin 

 (especially the lateral ridges) are the 

 serous glands. They are sunk deeper into 

 the dermis and are lined by a very flat 

 epithelium. Their function is probably to 

 make the animal distasteful to animals 

 which might prey on it. 



Turtle. This is the first dry skinned 

 animal we have studied. The epidermis 

 is thin and horny. The basal cells are 

 low cuboidal epithelium, which goes 

 over very quickly into thin squamous cells. 

 Several layers of these on the surface 

 have lost their nuclei and have become 

 cornified. This horny epidermis, produced 

 into folds, is what makes up the scales of 

 the reptiles, the dermis being also con- 

 tinued into the folds. However, the point 

 is that reptilian scales are epidermal 

 structures, whereas true fish scales are 

 dermal. It will be recalled that shark 

 scales are made up of both epidermal and 

 dermal elements. The dermis of the turtle 

 is very thick, consisting almost entirely 

 of dense white fibrous tissue. Just under 

 the epidermis it is quite vascular and 

 contains an abundance of chromatophores. 

 There are also occasional patches of pig- 

 ment granules in the epidermis. 



Chicken. The skin surface is much 

 folded and is interrupted frequently by 

 feather follicles. The epidermis is thin 

 and squamous, the outer layers being 

 cornified. The dermis consists of a thin 

 surface layer of dense fibrous tissue and a 

 thicker deep layer of loose areolar tissue, 

 containing blood vessels, nerves, touch 

 corpuscles (corpuscles of the Pacinian 

 type are frequent) and an abundance of 

 fat cells. No pigment is found in the 

 skin proper, but is restricted to the 



