ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 295 



the rudiment of the diaphysis of the tubular bones in mammals is a 

 stage which consists of laminre arranged concentrically round the whole 

 skeletal part. The interstices between these laminae are likewise con- 

 centric, and are occupied by a corresponding concentric network of blood 

 vessels. These spaces are later filled out with delicate non-lamellate 

 bone substance, which has a preponderatingly " in toto concentric " 

 arrangement, whilst, observed in detail, it is seen to be deposited 

 concentrically about the single vessel groups. This characteristic 

 arrangement, which persists in different animals for different periods, 

 entirely disappears, and is replaced by a structure formed of general 

 lamellte and Haversian pillars, which is likewise " in toto concentric." 

 Roux distinguishes the two stages as " primary" and " secondary in toto 

 concentric " respectively. The paper gives an account of the sub- 

 sequent changes resulting in the well-known compact diaphyses, as well 

 as the different degrees occurring in various animals and in particular 

 bones. 



Lumbar Spinal Cord in Birds.* — G. Imhof gives an account of the 

 structure and development of the lumbar spinal cord. The lumbar 

 dilatation, together with the widened pelvic canal, is a secondary acquisi- 

 tion of a relatively late period of embryonic life. It reaches in the histo- 

 logical differentiation of its supporting substance, a stage not possible 

 in modern reptiles, not to speak of Mesozoic forms. The author regards 

 the view that the lumbar swelling in birds is a character inherited from 

 Dinosaur ancestors as quite untenable. 



Notes on Opisthenogenesis.f — A. S. Packard discusses, with the 

 help of some examples which have come under his personal observation, 

 the question of the development of segments, median tubercles, and 

 markings a tergo. Opisthenogenesis, as regards markings, appears to 

 have some relation with the opisthenogenetic origin in post-embryonic 

 development of new segments in " the budding zone." The portion of 

 the animal which arises from this zone appears to be a secondary or 

 inherited region, due to the post-embryonic acquisition of new characters 

 (certain trunk segments and their appendages) in many segmented or 

 polymerous animals. It is suggested that the phenomenon of con- 

 crescence may be the initial cause, or at least in some way connected 

 with the breaking up of the longitudinal stripes of the body and their 

 transformation into spots at or near the budding zone of their poly- 

 merous or polypodous (Peripatus-Yike) ancestors. 



b. Histology. 



Studies on Neuroglia.:}: — W. Rubaschkin has investigated the origin, 

 nature, and relations of neuroglia, with the following results. It con- 

 sists of fibres and different kinds of cells genetically related. The 

 earliest gliagenetic cells are distinguished by their size and granular 

 cell-body with granular prolongations. The gliagenetic cells are the 

 beginning of all elements of the neuroglia, and form by the metamor- 



• Arch. Mikr. Anat., lxv. CI 905) pp. 498-610 (1 pi.). 

 t Proc. Amer. Phil. Soc, xliii. (1904) pp. 289-94. 

 X Arch. Mikr. Anat., lxiv. (1904) pp. 575-626 (4 pis.). 



