ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 59 



Differentiation of the Myotome.*— A. L. J. Sunier finds that the 

 undifferentiated elements of the wall of the myotome of Chordates are 

 differentiated half into muscular elenunts, and'half into mesenchvmatic 

 elements (connective in Acrania). 



The primordial elements of the musculature of Chordates are slab- 

 like cells, extending the length of the myotome, flattened more or less 

 dorso-ventrally, spreading more or less in a latero-median direction. 

 While this is going on the nuclei multiply, often if not always by ami- 

 tosis. Later on the slab-like cells are modified into fibres by longitudinal 

 fission. 



The formation of sclerotomic elements in Craniota is due to a dis- 

 solution of a portion of the median wall of the myotome. In Acrania 

 there is no such dissolution. The " sclerocoel "*of Selachians is the 

 space that remains between the median wall and the rounded ventral 

 end of the muscular mass. The sclerocoel of Cephalochorda is a special 

 adaptation, as Ziegler supposed. The term " external layer " may be 

 applied to the lateral wail of a hollow myotome, but what is called' the 

 external layer when the myotomes are solid, as in Murjenidae, is different, 

 and that of Cephalochorda is quite a special adaptation. 



Closure of Duct of Botallius.f — L. Stienon finds that the closure 

 of the duct of Botallius (between the aortic arch and the pulmonary 

 artery) after birth is a function of the aortic tension. The dilatation 

 of the isthmus brings about as a consequence the closure of the canal. 

 The closure is an instance of automatic adaptation. 



Experimental Study of Development of Limbs in Frog, t — B. 

 Diirken has made the experiment of extirpating the primordia of the 

 limbs at a very early stage in the development of the frog. The extir- 

 pation of one limb-primordium is usually associated with serious mal- 

 formations in the others. These are described in detail. There is also 

 a very interesting effect on the development of the spinal cord and 

 brain, the symmetry being much disturbed. From the affected nervous 

 system an influence is exerted on the other limbs not operated on. 

 There is a developmental correlation between nervous system and peri- 

 pheral organs. In this correlation the mid-brain seems to be of greatest 

 importance. 



Development of Sympathetic Nervous System in rrog.§ — Rene 

 Camus calls attention to the uncertainty that obtains in regard to the 

 development of the sympathetic nervous system. Remak and Goette 

 held it to be of independent mesodermic origin ; most of the recent 

 workers derive it from the ectoderm. But even on the latter view there 

 is great diversity of opinion. The cells which form the sympathetic are 

 derived from the spinal nerves, or from the spinal gangha, or from the 

 medullarv tube, or from the gangUonic ridge. 



The author finds that the fibrous differentiation of the nerve-tract 



* Tijdschr. Nederland. Dierkund. Yer., xii. (1911) pp. 75-182 (6 pis.). 

 + Arch. Biol., xxvii. (1912) pp. 501-14 (1 pi. and 2 figs.). 



* Zeitschr. wiss. Zool., xcix. (1911) pp. 189-355 (7 pis. and 18 figs.). 



§ Arch. Mikr. Anat., Lsxxi. (1912) Heft 1, Abt. 1, pp. 1-52 (4 pis. and 4 figs.). 



