-Q Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 



Variations in Internal Structures. 



In the study of the variations of internal structures only tliose which are most obvious have been 

 recorded. 



Notochord. 



There is considerable Variation in the anterior extent of the notochord in nearly all stages. This 

 Variation is more obvious in the earlier than in the later stages. Usually a considerable tract of mesenchyma 

 lies between the anterior end of the chorda and the hypophysis. Frequently this tract is short and sotnetimes 

 only a narrow band. 



Eye. 



In sections the optic vesicles show the same variations which have been recorded under variations 

 in external features. The appearance of pigment in the retina and iris shows considerable Variation. In 

 the 17 mm embryo series 140, 141, 145 show considerable pigment in the retina and its first appearance in 

 the iris, while 146 shows the beginning of pigment in the retina and none in the iris. The time of first 

 appearance of pigment in the choroid is likewise variable. In the 18 mm embryo series 152, 155 show 

 considerable pigment, series 146, 151 show but little pigment, while in series 147, 149, 150 there is no 

 pigment in the choroid. 



Ear. 



In the 6 mm embryo, series loo, there is a cup-shaped invagination of the inner layer of the ectoderm 

 while in series loi there is a vesicle. In the 7 mm embryo, series 102, shows the otic vesicle just closed, 

 while in .series 103 it is not quite closed. In the 18 mm larva, series 146 and 147, the endolymphatic duct 

 extends over the medulla to about one half the distance to median line; in series 151 it extends over the 

 lateral margin of the medulla; in series 149 it does not extend over the lateral margin of the medulla. 



Nose. 



In the 9 mm stage series 106 shows the anläge of the nose as a shallow invagination of the ectoderm. 

 In series 107 there i.s no invagination. In 108 it is slightly cup-shaped. In series 109 thickened ectoderm, 

 in series iio thickened ectoderm. 



Bpiphysis. 



In the 9 mm stage series 106, 109, 108 show the epiphysis to be a slight cup-shaped evagination in 

 the dorsal wall of the fore-brain. In series 107, iio the evagination is deeper and somewhat pear-shaped. 



Paraphysis. 



In the II mm embryos, series Il6, the paraphysis is a very shallow evagination in tlie postero-dorsal 

 wall of the telencephalon. In 117 the paraphysis is a deep pit-like evagination. 



