362 SUMMA.BY OF CURRENT RESEARCHES RELATING TO 



Development of Teleostei.* — C. Kuppfer continues his studies on 

 the development of the Vertebrata, and treats of the Teleostei. Two 

 varieties of trout were selected for study. The blastoderm on the 

 eighth day presented a round area with a prominent knob at the 

 posterior extremity (^Schwanzknospe) ; in front of this lies the embry- 

 onic shield. The next step is an invagination upon the surface of 

 the latter, exactly as in birds and reptiles, forming a longitudinal 

 furrow which subsequently is crossed at right angles by another 

 furrow ; this transverse furrow is only a temporary structure, and 

 presently vanishes, leaving only the longitudinal furrow ; at the hinder 

 end of the primitive streak, its margins unite to form a median axial 

 band, which extends as far as the caudal knob. By the beginning of 

 the twelfth day the primitive streak had disappeared, and the axial 

 band a little wider at its anterior extremity occupied the middle line 

 of the embryonic shield coinciding exactly with the anterior extremity 

 of the primitive streak. The disappearance of the primitive streak 

 coincides in point of time with the enclosure of half the yolk within 

 the blastoderm ; when the cells of the blastoderm pass beyond the 

 equator of the egg, the primitive streak is entirely replaced by the 

 axial band. 



At the time of the appearance of the head, the axial band becomes 

 slightly coiled ; the " head " consists of the rudiment of the brain and 

 eyes, and one pair of visceral arches ; it is developed independently 

 of the primitive streak ; though the brain is continuous with the axial 

 band, it is marked off from it by a constriction. The provertebree 

 which next appear are formed from the axial band, and the anterior 

 ones are developed before the posterior ones ; in many other Teleostei 

 the first pair of protovertebr^ are situated more in the middle and the 

 process of growth extends forwards as well as backwards. No other 

 pairs of visceral arches are developed in the neighbourhood of the 

 first. The earliest rudiment of the spinal cord appears as a new 

 formation upon the axial band, and is continuous with the brain ; the 

 central cavity of both, which is a secondary formation, commences in 

 the eyes and passes down the brain into the spinal cord ; this central 

 cavity shows widenings here and there in the brain which do not 

 correspond to the subsequently formed ventricles. 



Influence of High Pressures on Living Organisms.t — P. Regnard 

 has been able to make some experiments with a press giving a pressure 

 of 1000 atmospheres ; he finds that under such pressures as obtain on 

 the bed of the ocean, plants, infusoria, molluscs, annelids, and Crustacea 

 fall into a somnolent condition, or one of " latent life " ; fishes, when 

 exposed to similar pressures, die. Experiments made show that 

 muscles of the frog increase in weight after being subjected to a pres- 

 sure of 400 atmospheres, but it is not yet known whether this change 

 is chemical or physical. 



Interesting points of resemblance are to be detected between these 

 results and those obtained by the ' Talisman ' deep-sea explorations ; 



* Arch. f. Anat. u. Physiol. (Auat. Abtheil.), 1884, pp. 1-40 (2 pis.), 

 t Comptes Kendus, xcviii. (1884) pp. 745-7. 



