STRUCTURE AND DEVELOPMENT OF COELOPLANA. 59 



later even to have a gliding movement, using the extended pharyngeal 

 surface as the sole (fig. 14). The appearance of the larva performing 

 such locomotion recalls distinctly that of Lampetia in similar attitude, 

 taking of course no account of the great difference in size in the two 

 forms. It is usually the case with the larva in this stage that after a 

 short time of crawling, it recommences swimming about by means of 

 comb-plates, but again, before very long, sinks to the bottom to return 

 to crawling, thus performing the two modes of locomotion practically 

 alternately. The structure of the larva at this stage differs in no way 

 from that of the time of the liberation, except some slight changes 

 undergone by certain organs or tissues such as: — all kinds of pigment 

 spots have increased considerably in all parts of the body, rendering the 

 examination of internal structure almost impossible, especially spots 

 coloured brownish are found in quantities in the regions adjoining the 

 mouth, the tentacular apparatuses and the sense-organ : the spots looking 

 opaque by transmitted light that have been scattered here and there 

 without order up to this time, now are distributed evenly throughout 

 the surface of the body : the gape of the mouth has become much 

 wider than before. The oral part of the body is capable of great 

 change in shape by means of muscle-fibres developed therein. 



In the next four or five hours, most of the cilia of the comb-plates 

 become either bent or broken off in the middle or even fall off, showing 

 clearly that the degenerating change of those swimming apparatuses 

 has already set in, so that the larva becomes entirely incapable of 

 swimming, although the remaining cilia still continue to beat as before. 

 The tentacles grow longer and develop new accessory filaments, while 

 the sole of the extended pharynx spreads out very widely all around. 

 Sooner or later, the cilia fall off entirely; the sole becomes enlarged 

 extensively in all directions, and is flattened out in an almost film-like 

 manner (fig. 15). The larval body in this state consists of two distinct 

 parts, a broad and thin basal expansion and a hump- like elevation in 

 the centre of it, of which the former has been transformed from the 

 part of the body around the external half of the pharynx and the latter 

 from the parts above it. Unfortunately I could observe a single specimen 

 to undergo metamorphosis and the specimen died when the condition 

 just described was attained, but it is easy to imagine that by gradual 

 depression of the elevation just mentioned, the entire body would assume 

 the habitus of the adult. 



Of the individuals that have completely transformed into the adult 



