ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 19 



blood-cells, and supporting tissue. The liver is at first a predominantly 

 erythropoietic organ, and the author gives a circumstantial account of 

 its activity. 



Development of Head of Gymnophiona.* — Harry Marcus con- 

 tinues his study of Hypogeophis embryos. The most anterior roof of 

 the archentcron consists of vegetative cells, and here, in contrast to the 

 trunk, the notochord has an endodermic origin, and there are typical 

 mesodermic coelom-cavities. The development of the head-cavities and 

 the mesoderm is described, The columella auris arises from the hyoid 

 arch, and is clearly separable from the auditory capsule blastema. The 

 stapedial artery, which passes through the stapes in Ichthyophis is a 

 branch of the second aortic arch. A corroboration of the homology of 

 stapes and hyomandibular is found in the course of the 7th and 8th 

 nerves. The author also describes the formation of the cerebral ganglia. 



Abnormal Reproductive Organs in Frog.f — AV. Youngman de- 

 scribes an interesting case — a large specimen of Rana temporaria. It 

 had small thumb-pads, a normal ovary on the left, an ovo-testis on the 

 right, two normal oviducts with eggs in them, normal ureters, no trace 

 of vasa efferentia or seminal- vesicles. The correlation of the two male 

 characters suggests that the thumb-pad is the outcome of a physiological 

 secretion in some way connected with the male sexual elements. 



Spermatogenesis of Fowl.! — M. F. Guyer finds that accurate 

 •enumeration of the spermatogonial chromosomes is very difficult. 

 Seventeen is probably the correct number, but it is safer simply to say 

 that there are not less than fifteen, not more than nineteen. 



Nine chromosomes ordinarily appear in the prophase of the first 

 division of the spermatocytes. Of these, eight are presumably bivalent. 

 The other, which is the " odd " or " accessory " chromosome, has not 

 paired at this time, but is nevertheless probably a compound body 

 consisting of three elements. 



The odd chromosome not infrequently reveals a tripartite structure. 

 Less often one of its components seems to stand more or less apart, like 

 ■a " supernumerary " chromosome. The odd chromosome passes un- 

 divided to one pole in the vast majority of cases, so that one daughter- 

 -cell receives eight and the other nine chromosomes. 



In the second division of the spermatocytes the eight chromosomes 

 of the former division pair to form four chromosomes. Likewise, eight 

 of the nine which passed to the other daughter-cell pair to form four, 

 but the odd one remains unpaired. In this second division the odd 

 •chromosome, after lagging somewhat, divides, and thus there are formed 

 two spermatids each containing five chromosomes. The spermatids 

 formed from the division of secondary spermatocytes which contained 

 but four chromosomes, receive only four chromosomes each. Thus the 

 final result of the two divisions of the spermatocytes is the production of 

 four spermatids, two of which receive four, and two five chromosomes. 



* Morphol. Jahrb., xl. (1909) pp. 105-83 (3 pis. and 37 figs.). 

 t Anat. Anzeig., xxxv. (1909) pp. 301-3 (3 figs.). 

 X Tom. cit., pp. 573-80 (2 pis. ). 



c 2 



