402 



SCIENCE. 



[N. S. Vol. XII. No. 298. 



consists of a series of ten spots along the 

 region of the alimentary canal and lower 

 part of the tail, a black spot about the end 

 of the tail and another at the tip of the 

 lower jaw, with a few cells on the upper 

 jaw. 



Especially noteworthy is the develop- 

 ment of enormous fang-like teeth, four pairs 

 in each jaw. The upper decrease in length 

 from the front backwards, while those of the 

 lower jaw are nearly of uniform size. 



When first hatched the larvse floated verti- 

 cally, near the surface, heads up, tails down. 

 Later they assumed the horizontal position 

 and explored all parts of the vessel in which 

 they were contained, progressing in ap- 

 proved eel fashion and biting at nearly 

 everything touched. 



The evidence that the eggs are those of 

 the Conger is not positive. If Grassi is 

 right, these eggs cannot belong to the 

 common eel. The Conger eel is the only 

 other one abundant in the region in which 

 the eggs were collected and was caught in 

 numbers at the time the eggs were col- 

 lected. The serious objection to referring 

 them to the Conger is the large number of 

 segments in front of the anus. Since, how- 

 ever, according to Grassi, the anus mi- 

 grates to near the end of the tail during the 

 changes to the Leptocephalus stage, the 

 number of segments in front of the anus is 

 probably not positively available in the 

 identification of the larva. 



Carl H. Eigenmann. 



Woods Holl, Mass., August 25, ]900. 



SEAT-ENQINE DIAGRAMS. 

 The accompanying diagram, in which are 

 shown the possible compositions of the four 

 standard thermodynamic, lines in the for- 

 mation of heat-engine diagrams or thermo- 

 dynamic cycles, has been found so useful 

 during twenty years' experience in its em- 

 ployment that it has seemed possible that 



it may prove deserving of extended publi- 

 cation. It has just been engraved in this 

 particular form for illustration of a new edi- 

 tion of the ' Manual of the Steam-engine.' 

 Gas-engine cycles are seen to number no 

 less than seventeen, of which a large pro- 

 portion are mechanically and kinematically 

 practical, and a half-dozen of which have 

 been adopted or designed by engineers. 



The Carnot, or Sterling — I, ah e d — and 

 its equivalent, ah n m, or V, the regenera- 

 tor cycle, only, it is recognized, can yield 

 maximum efficiency, as a thermodynamic 



proposition ; but the Joule, or Brayton, and 

 the Ericsson, among the gas-engine cycles 

 and the Eankins and Clausius among vapor- 

 engine cycles have been found available by 

 designers and builders, and it is probable 

 that, among the infinite number of con- 

 ceivable cycles outside the class here illus- 

 trated, many may be found capable of 

 meeting the demand of the engineer for a 

 practical union of thermodynamic, me- 

 chanical and kinematic closed cycles. 



The production of the cycle of Carnot is 

 not a difficult task as a matter of design 

 but, in the case of the gas-engine, it in- 

 volves too extensive a variation of volume 

 to find place in application. It is far more 

 practicable with vapor-engines and Cotterill 

 long since suggested a practical approxima- 

 tion of which the engineers of our own day 

 are beginning to avail themselves. 



R. H. Thurston. 



