No. 482] NOTES AND LITERATURE 



133 



Of the stages after the closure of the medullary folds the accounts 

 are far less detailed than we could wish and there are many gaps in 

 the organogeny which remain to be filled but which cannot at present 

 be described on account of lack of material. Especially interesting 

 are the figures given of a reconstruction of the skull of a well advanced 

 embryo in which the pterygoquadrate bar is not completely fused 

 with the cranium. Other features of organogeny given are concerned 

 with (1) the integument and dentition in which embryos and larvae of 

 other chimseroids are considered and the conclusion is reached that 

 the dental plates represent fused denticles. (2) The skeleton which is 

 largely based on the work of Schauinsland. (3) The viscera. There 

 is, even in early stages, no continuous mesentery. A few words are 

 devoted to gut, gills and nephridial structures. 



The third section, one of the most valuable of the work, is a discus- 

 sion of the fossil chimseroids. The existence of Silurian members of 

 the group is more than doubted, but, as shown by the Ptyctodonts, 

 they probably occurred in the Devonian. The definite knowledge of 

 the group began with the lower Jurassic, since which time numerous 

 undoubted chimseroids have occurred, the group attaining its maxi- 

 mum development in the cretaceous. Thvsv fossils and The stnictnrc 

 and embryology of the existing species arc invoked to show that the 

 chimffiroids are not a primitive group but are a ino(HHed and >|)eeiahz( d 

 development from forms more like the normal Selacliiaiis. An rwvu- 

 sive bibliography closes the volume. 



.1. S. K. 



Development of the Mammalian Lung. Flint (Am. Journ. Anat. 

 6, 1906) describes in a l(Mig ])aper the development of the lung and 

 associated structures in tlie pig Tlie anlage is asymmetrical, and its 

 origin, below the level of the gill pouches is an argument against any 

 phylogenetic connection between lungs and gill pouches. The develop- 

 ment of the bronchi is followed in detail and many variations noted, the 

 complete series including sixteen on one side and seventeen on the 

 other, a condition rarely occurring. iEby's conclusion that the pul- 

 monary artery differentiates two lung regions of different morphologi- 

 cal significance is not supported. The pulmonary veins arise as an 

 outgrowth from the undivided portion of the sinus venosus, the veins 

 to the right and left lungs developing by specialization in the capillary 

 plexus. In the eaiHer history the division of the respiratory ducts is 

 monopodial in ( haracter as in the lower pulmonate vertebrates and it 

 is only in the other stages that dichotomous division, characteristic 



