ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 21 



carried further by what has been observed with regard to the origin 

 and history of the foot-cells of the testis. He is forced to the con- 

 clusion that either the leucocytes themselves or their immediate ancestors 

 may give rise to connective tissue, the former probably being what 

 really happens. It is pointed out that one of the earliest phenomena 

 observed in the development of cancer is the fusion of a leucocyte 

 with a tissue-cell, and the subsequent division of the cell resulting from 

 the fusion into two daughter-cells, each possessing chromatic elements 

 derived partly from the leucocyte, and partly from the tissue-cell. 

 Among the cells of malignant growths all the forms of division re- 

 corded in this paper for leucocytes and their immediate ancestors are 

 to be found. 



Aortic Arches in Vertebrates.* — W. C. Locy has succeeded in 

 injecting a number of chick-embryos of between four and five days, and 

 by this means has clearly demonstrated that the fifth arch is an anterior 

 offshoot of the sixth. It is a veritable aortic arch, agreeing histo- 

 logically in all essential features with the other arches. Its period of 

 existence is, however, much briefer, and it is also subject to greater 

 individual variation. The author comments on the condition of the 

 fifth and sixth arch in other vertebrate groups ; he considers that 

 while vascular elements exhibit greater variabihty in their stages of 

 formation and degeneration, there are recorded a sufficient number of 

 cases of their aggregation into a complete vessel to justify the assump- 

 tion that there is a fifth aortic arch in mammals as in other Vertebrates. 



Development of Human Thorax.t — Charlotte Muller, by means of 

 reconstruction models, has investigated the characteristics of the thorax 

 in very early embryos. She distinguishes purely embryonal and em- 

 bryonal atavistic characters. Of the former, the most interesting 

 feature is the contraction in the lateral wall ; of the latter is the trans- 

 itory keel form, which is limited to the proximal region of the thorax. 

 This keel formation is very widely found amongst lower mammals ; it 

 is replaced in the primates by the dorso-ventral flattening. This stands, 

 in relation to the upright position and the freer development of the upper- 

 extremity. In the human embryo the thorax has a greater dorso- 

 ventral than transverse diameter. 



Placental Syncytia. + — H. Strahl has examined the placenta in a 

 number of types, e.g. Myrmecophaga, Dasypus, Aluata caraya Humb., 

 and finds an unusual development of syncytial villi, probably of 

 importance in the nutrition of the foetus. These forms exhibit an 

 interesting resemblance to the human placenta. 



Uterus of Hedgehog after Parturition.§ — H. Strahl finds that 

 when the puerperal involution of the uterus of the hedgehog is com- 

 pared with the same process as it occurs in other mammals, the 

 hedgehog occupies an intermediate position between Rodents and 

 Carnivores. " It stands near the former in the way in which the 



* Anat. Anzeig., xxix. (1906) pp. 287-300 (10 figs.). 



t Morphol. Jahrb., xxxv. (1906) pp. 591-696 (21 figs.). 



X Anat. Anzeig., xxix. (1906) Ergauzungsheft, pp. 69-73. 



§ Proo. Section Sciences K. Akad. Amsterdam, viii. (1906) pp. 812-14. 



