Aug. 17, 1888.] 



SCIENTIFIC NEWS. 



14/ 



scope is necessary to make out its structure. It has a 

 long transparent body, traversed by a simple ali- 

 mentary canal, and provided at the head end 

 with a crown of ciliated tentacles. Close to the 

 other end is a ciliated ring. This condition is well 

 suited to dispersal, and some kind of locomotive larva is, 

 as we have more than once pointed out, a very common 

 phase in the life-history of marine animals. But the 

 adult form of our ciliated embryo is a tube-dwelling 

 worm, known as Phoronis. The passage from the 

 Actinotrocha to the Phoronis condition presents certain 

 difficulties, which have been overcome in an interesting 

 way. At first the intestineisstraight, as in most worms, but 

 this arrangement does not suit an animal which lives 

 in a tube without outlet below. Accordingly the worm 

 seems to have been led in the first instance to double 

 itself up, so that the intestine ended at the mouth of the 

 tube. In such worms as Sabella this simple resource 

 persists without modification. One serious inconvenience 



and fittings, without stopping work for a single day. 

 Others, like many insects, which lie up for a time as 

 motionless pupae, resemble the shopkeeper, who shuts 

 up for a month in order to clear out his old stock and 

 furniture. But Phoronis must be compared to the man 

 who means to make his shop-door in a new place and 

 add a room or two at the same time. He has all ready ; 

 all the new walls, and floors, and passages are complete, 

 down to the door-knobs, and at last there is nothing 

 needed but to shut one door and open another. 



THE WILLIAMS SINGLE CYLINDER 

 AUTOMATIC CUT-OFF ENGINE. 



'"PHIS engine has achieved such remarkable results as 



to attract the attention of leading engineers in the 



United States, so we propose giving a brief description of it. 



As will be seen from our illustration, borrowed from 



the Illustrated World, the proportions are graceful, and 



results. The alimentary canal, and the whole body, are 

 reduced by doubling to one-half of their original length 

 — a great disadvantage to any animal which has to reach 

 out of its burrow in search of food. Phoronis has solved 

 the problem in a neater way than Sabella. It prepares 

 beforehand a pouch opening on the side of its body near 

 the head. This pouch gradually lengthens, and the tip, 

 which, of course, is innermost, attaches itself to the 

 slowly elongating intestine, which lies loose in the body 

 cavity. When the moment of transformation comes, the 

 pouch turns itself inside out, like a stocking drawn 

 hastily off the foot, and henceforth constitutes the chief 

 part of the body of the worm. The alimentary canal is 

 at once drawn into it, and thus becomes suddenly bent 

 into a loop, whose two ends are brought together at the 

 mouth of the tube. In a quarter of an-hour the Phoronis 

 is completely adapted to its new conditions. 



Some animals, while undergoing transformation, 

 change their bodies and their mode of life by insensible 

 degrees, like a tradesman who gradually alters his shop 



all the wearing surfaces very ample and of the best 

 material. The distribution of steam and weight forces 

 upon the bearings has been carefully calculated, so that 

 no unnecessary strains shall be brought on any part. ,*• 

 One of the most valuable features, and one which is 

 quite novel to engineering practice, is a construction of 

 pressure plates which admits steam on their undersides, 

 counteracting in a large part the pressure on their backs. 

 No injury to the valve faces, therefore, can result from 

 letting the plates "down hard " upon the valves, and when 

 so adjusted the " high " portions of the faces will wear 

 gradually away under the light pressures upon them, and 

 the leakage, if there be any, will cease. When the wear 

 has equalled the amount the plates were let down the 

 plates will bear wholly on distance ledges at their ends, 

 and the valves move freely under them. This feature 

 furnishes an easy, safe, and sure means of keeping the 

 valves tight. These pressure-plates do not, therefore, 

 require that refinement of accuracy in fitting and adjust- 

 ing which has been considered objectionable to other 



