310 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the layer of the rods compact." He does not as yet apply this con- 

 clusion outside the Amphibia, not being convinced that the "cones'' of 

 the Vertebrate retina are necessarily identical structures throughout 

 the phylum ; but he believes that the minute differences recorded by 

 the various histologists who have studied the retina will prove to be 

 due to the fact that different physiological cunditions induce distinct 

 structural differences. 



Bursa Entiana of Selachians.* — Dr. H. C. Eedeke discusses the 

 exact meaning of this term, in regard to which he believes considerable 

 confusion exists. The true bursa entiana is a small area of the stomach 

 at the anterior end of the pars pylorica, and is present only in Galeus 

 canis. In some sharks and many rays the spiral valve of the intestine 

 is confined to the posterior region of the mid-gut, so that between the 

 pylorus and the region where the valve begins there is an intermediate 

 valveless area which has been erroneously supposed to be the bursa 

 entiana. This area may be called tween-gut (Zioischendami), and is 

 absent in most Selachians where the spiral valve begins immediately 

 behind the pylorus. 



Tooth-plate of Cyprinoids.f — Valerian Gratzianow has investigated 

 the histology of the remarkable horny plate found in these fish. He 

 finds that it is an epidermal structure, consisting of large polygonal 

 cells which readily take up stains. At its base are a number of con- 

 nective-tissue papilla?, recalling the similar structures found in the 

 horny plates of OrnitJiorhynchus. In one case (in the telescope fish) at 

 the summit of certain of the papillae sensitive bulbs similar to taste-buds 

 were found. The author can only explain this remarkable circumstance 

 as due to atavism, and suggesting that the masticatory plate is a recent 

 acquisition. In certain of the Cyprinoids the tooth-plate arises by a 

 simple differentiation of the gullet epithelium ; but in Carassius and 

 Cyprinus its origin is somewhat more complex, recalling the development 

 of a true tooth. Further details of structure and development are 

 promised. 



Micro-crystals of Vertebrate Blood.J — Herr H. U. Kobert discusses 

 the micro-crystallographic behaviour of vertebrate blood at some length 

 and in considerable detail. His observations are rather critical than 

 novel, though they give evidence of much personal work and assiduity. 

 The author discusses the crystalline and crystalloid appearances found in 

 the various conditions of blood and its constituents, much space being 

 devoted to the important haBinin crystals. The article includes remarks 

 on Charcot's crystals, blood-serum crystals, fibrin-crystals, and formalin- 

 pigment crystals. The illustrations are somewhat crude and diagram- 

 matic, but may be accepted as faithful delineations of the appearances 

 described. 



c. General. 



Artificial Production of Rhythmic Muscle Contractions^ — Prof. J. 

 Loeb has found that certain solutions containing ions of sodium, chlorine, 



* Anat. Anzeig., xvii. (1900) pp. 1*46-59 (3 figs.). 



t Zool. Anzeig., xxiii. (1900) pp. 66-73 (5 figs.). 



t Zeitschr. f. arigew. Mikr., v. (1899) pp. 157-72, 185-200, 213-28, 241-6 (39 figs.). 



§ Festschr. A. Fick, 1899, pp. 101-19. See Amer. Nat., xxxiv. (1900) p. 150. 



