Cell Lamination of the Cerebral Cortex of Echidna, etc. 113 



Figs. 37 and 38. — Two stages of segmentation mitoses. 



Figs. 39 to 48 represent eggs of the spring generation. 



Fig. 39 a, b. — Two successive sections of chromosome group at edge of egg before 



maturation division. 

 Fig. 40. — Early stage of maturation division. 

 Fig. 41. — Late stage of maturation division. 



Fig. 42. — Completion of maturation division. Chromosomes of egg-nucleus sinking in ; 

 polar chromosomes in two groups. 



Fig. 43 a, b, c. — Polar chromosomes and egg-nucleus, a and b, successive sections of 

 polar chromosomes ; c, egg nucleus several sections removed. ( x about 800.) 



Fig. 44 a, b. — Two equatorial plates of segmentation mitoses, showing about 20 chromo- 

 somes. 



Fig. 45. — Prophase of segmentation mitosis, showing numerous long coiled chromosomes. 

 Fig. 46 a, b, c. — Metaphase (a), early (6), and late anaphases (c) of normal segmentation 



mitoses with diploid number. 

 Fig. 47. — Equatorial plate in face of segmentation mitosis with haploid number. 

 Fig. 48 a, b, c. — Metaphase (a), anaphase (6) in side view, and anaphase in pole view (c) 



of segmentation mitoses with haploid number. 



Preliminary Note upon the Cell Lamination of the Cerebral 

 Cortex of Echidna, tvith an Enumeration of the Fibres in the 

 Cranial Nerves. 



By Edgar Schuster, D.Sc, Fellow of New College (Pathological Laboratory, 

 Claybury Asylum, Essex, and Department of Comparative Anatomy, 

 University Museum, Oxford). 



(Communicated by Dr. F. W. Mott, F.R.S. Received September 30, — 

 Read December 9, 1909.) 



[Plates 4 and 5.] 



Material. — The following notes are based on the study of the brain of an 

 Echidna which died in the gardens of the Zoological Society in London. 



Dr. F. W. Mott, F.R.S., kindly placed the brain in my hands with the 

 suggestion that I should examine the cell lamination of the cortex and should 

 estimate the numbers of fibres in the cranial nerves. For this and for his 

 advice and help during the investigation I wish here to express my 

 gratitude. 



The right hemisphere was cut transversely into a series of sections 10 fi in 

 thickness, from which sections were taken at intervals of about \ mm., 

 stained with polychrome blue, and mounted. It may, perhaps, be mentioned 



