94 



J. BEARD, 



along the inner side of the ridge, but along its central portion. The 

 examination of a pig- or rabbit-embryo , corresponding to Keibel's 

 figs. 26 and 27 of the "Normentafel" will convince anyone of the 

 truth of this. But — and this is the crucial point — Klaatsch 

 himself (rightly) derives the marsupium from the mammary pockets, 

 and he distinctly postulates the mammary pockets as the forerunners 

 of the pouch (in: Morph. Jahrb., V. 17, p. 487), the latter being with 

 regard to the former a secondary structure. 



This being so, it would seem to follow, that the mammary pockets 

 must first be laid down in the development — as they unquestionably 

 are in the forms described in this paper — before a pouch can arise 

 from them. 



Klaatsch assumes this to hold good for marsupials, but, when 

 he comes to interpret the developmental facts of Eutheria, such as 

 pig and rabbit, he reverses the order of events, and makes the rudi- 

 ment of the pouch, his "marsupial ridge", arise before the milk-points 



Table of Characters of late uterine and 



Form of body 



Chorda and 

 vertebral 

 column 



Nervous 

 system 



Eye 



Nose 



Body fonijilete ex- 

 ternally. Head 

 bent. Mouth open. 

 Arms somewhat 

 flexed. Digits of 

 hand marked and 

 clawed. Hind limbs 

 imperfect. Digits 

 barely indicated. 



Body complete 

 and like that of a 

 mammal. The ani- 

 mal much resem- 

 bles a new-born 



opossum. Head 

 raised. Arm quite 

 pronated. Digits 

 andclaws very pro 



nouDced. Hind 



limbs etc. much as 



in preceding. 



Chorda small. 

 Marked carti- 

 laginous arches 

 and centra in 

 neck and 

 thorax. 



Marked con- 

 striction of 

 chorda. Neural 

 arches almost 

 complete. 



Formation of 

 posterior 



fissure not yet 

 initiated. 



Lietina half 

 pigmented. 

 Cellular lens. 



Formation of 



post, fissure 



well initiated. 



Ketina half 

 pigmented. 

 No rods and! 

 cones. Form 

 ation of lens 

 fibres. 



Jacobson's 

 organ form- 

 ed. Cho- 

 ana open. 



As in pre- 

 ceding. 



