Ear and Nose 



423 



enchyme which constitutes much if not all 

 of the orthotopic capsule arises from mesen- 

 toderm of the ear region and the anterior 

 somites (Stone, '26; Kucherova, '35; Ichi- 

 kawa, '36; Kaan, '38). 



The ear vesicle has the ability to draw 

 mesenchymal cells toward it (Filatow, '27). 

 In the flank these may be from sclerotomes 

 and form capsule, or they may be from other 

 sources and organized into a more or less com- 

 plete limb. In the orthotopic position cells 

 so attracted form the normal capsule (Kaan, 

 '38). If other structures such as nasal placode, 

 optic cup, or lens placode are substituted for 

 the otic vesicle, no cartilaginous capsule 

 forms (Lewis, '07; Ichikawa, '36; Kaan, '38). 

 Orientation of mesenchymal cells about a 

 celloidin block in the ear region has been 

 reported (Filatow, '27). 



FORMATION OF MIDDLE EAR 



Effects of absence of the inner ear upon 

 the development of the middle ear in Rana 

 have been observed by Luther ('24) and 

 Violette ('28, '30). The tympanic ring and 

 membrane as well as the middle and external 

 parts of the columella develop independ- 

 ently of the inner ear. The inner end of the 

 columella and the operculum are dependent 

 on the presence of a normal labyrinth for 

 their full development but only the oper- 

 culimi is absent when this factor is removed. 

 In the chick, formation of the stapedial plate 

 depends upon presence of the inner ear: the 

 remainder of the columella forms after 

 extirpation of the otic vesicle (Reagan, '17). 



The metamorphic transformation of the 

 frog ear has been described by Witschi ('49). 

 Formation of the tympanic membrane of 

 the frog depends upon the presence of the 

 annular tympanic cartilage (Helff, '40). The 

 quadrate, another visceral cartilage, can also 

 induce formation of the membrane if in 

 contact with the skin. A cartilage of the 

 appendicular skeleton is less effective. The 

 induction is probably brought about by some 

 chemical product of the cartilage, since the 

 tympanic cartilage still retains inductive 

 influences after being killed by various 

 methods. 



THE NOSE 



DIFFERENTIATION OF THE NASAL 

 PLACODE 



Studies on the development of the nasal sac 

 show that it undergoes the typical embryonic 

 process of a gradually increasing differentia- 



tion along with a progressive loss by the 

 embryo of the ability to constitute the organ 

 from adjacent tissue. 



Early differentiation of the nasal rudiment 

 has occurred by the early neurula stage in 

 Ambly stoma (Carpenter, '37) and in Rana 

 (Zwilling, '40); this has been demonstrated 

 by heterotopic transplants. Nasal sacs inde- 

 pendent of brain tissue may form from pro- 

 spective ectoderm of the middle gastrula 

 when transplanted to a blastema (Emerson, 

 '45). This result may indicate a determina- 

 tion on the part of the ectodermal rudiment 

 or may be due to an inductor in the ab- 

 normal environment. In any case differentia- 

 tion of the nasal rudiment does not wait 

 upon formation of the neural plate and folds 

 and its induction may start during gastrula- 

 tion, as does that of the ear. 



During neurulation and later stages the 

 rudiment acquires greater power of self- 

 differentiation (Kawakami, '36; Zwilling, 

 '40). Following extirpation of the nasal 

 rudiment diiring neurular and head process 

 stages, a new sac develops from the replac- 

 ing ectoderm (Bell, '06; Lima, '15). This 

 ability is subsequently lost (Burr, '16). Belly 

 ectoderm of the early neurula has the ability 

 to form a normal olfactory sac (Kucherova, 

 '45). The formation of the nasolacrimal duct 

 depends upon the presence of the nasal pit 

 (Ogawa, '29). 



INDUCTION OF THE NASAL PLACODE 



The problems concerned with the induc- 

 tion of the nasal sac are peculiarly like those 

 of the ear vesicle; they involve the questions 

 of a mesodermal and subsequent neural in- 

 duction. 



Considerable evidence points to the pres- 

 ence of an early mesodermal induction of 

 the nasal sac: (1) the more normal differen- 

 tiation in explants (Emerson, '45) and heter- 

 otopically (Luna, '15; Cooper, '43) in pres- 

 ence of underlying mesoderm; (2) induction 

 of sac by mesoderm with no induced brain 

 (Zwilling, '40; Moore, '46; Kawakami, '43), 

 and induction of sacs which have no connec- 

 tion with brain parts, as in Bufo by Triton 

 (Holtfreter, '36); (3) differentiation in situ 

 of nasal organs after removal of anterior 

 neural plate (Spemann, '12; Raunich, '50); 

 (4) formation of a nasal organ following re- 

 moval of anterior neural fold and olfactory 

 rudiment, and its absence if underlying 

 mesoderm is included in the extirpate 

 (Siggia, '36); (5) the demonstration of dif- 

 ferentiation of the rudiment prior to forma- 



