28 



INTRODUCTION PROTOPLASM ELL 



mental germ layers: ectoderm (ectoblast; epiblast), mesoderm (meso- 

 blast),, entoderm (endoblast; hypoblast) have appeared (Fig. 32). Back 

 of this of course must lie a more fundamental differentiation, perhaps 

 already present in the unfertilized egg, a predelineation of adult struc- 

 ture destined to develop from localized egg materials. By the process of 

 histogenesis all the adult tissues arise from the several germ layers. This 

 matter is summarized in the following table : 



ADULT TISSUE DERIVATIVES FEOM 



ECTODERM 



Epidermis and its de- 

 rivatives : hair, nails, 

 and epithelium of se- 

 baceous, sweat and 

 mammary glands. 



Epithelium of mouth 

 and its derivatives : 

 enamel, taste buds, 

 epithelium of salivary 

 and other b u c c a 1 

 glands, and anterior 

 portion of hypophysis. 



Epithelium of anus, 

 and distal portion of 

 the male urethra. 



Epithelium of nos- 

 trils and communicat- 

 ing glands and cranial 

 sinuses. 



Epithelium of con- 

 junctiva and associated 

 ducts and lacrimal 

 glands. The lens, and 

 the epithelium of the 

 pars nervosa, ciliaris 

 and iridica retinae. 



Epithelium of mem- 



MESODERM 



Epithelium of urinif- 

 erous tubules, renal 

 pelves and ureters. 



Epithelium of the 

 seminiferous tubules 

 and the associated ex- 

 cretory ducts of the tes- 

 tis; epithelium of ovi- 

 duct and uterus; prob- 

 ably also the sex cells. 

 The cortex of the su- 

 prarenal gland. All 

 muscular tissue ; con- 

 nective tissue ; vascular 

 tissue (blood and 

 lymph vessels and 

 cells), and lymphoid 

 organs in general. 



Epithelium (meso- 

 thelium) of pleurae, 

 pericardium and peri- 

 toneum; of the tendon 

 sheaths, joint cavities 

 and bursse; and of the 

 chambers of the eye, 

 and the perilymph 

 spaces of the internal 



ENTODERM 



Epithelium of diges-. 

 tive tract (including 

 pharynx; excluding 

 mouth and anus) and 

 associated glands: 

 pharyngeal, esophageal, 

 gastric, intestinal, pan- 

 creas and liver, with 

 gall-bladder. 



Epithelium of middle 

 ear (tympanum) and 

 auditory (Eustachian) 

 tube. Epithelium of 

 respiratory system, be- 

 yond nostril. Epithe- 

 lium of thyroid, para- 

 thyroids, and the thy- 

 mic reticulum and cor- 

 puscles. 



Epithelium of female 

 urethra, proximal part 

 of male urethra, and of 

 the urinary bladder. 



Epithelium of pros- 

 tatic and Cowper's 

 glands in the male, 

 and of the glands of 



