338 ROREN AND DANIELSSEN ON THE 



by the strong muscular contractions which it presents. A little 

 later, the stomach and the oesophagus appear ; the latter pre- 

 sents itself under the form of a hollow cylinder attached to the 

 proboscis, and presenting upon its parietes, which are of excess- 

 ive thinness, a certain number of clear striae, the rudiments of 

 the future muscular tubes. As soon as the oesophagus becomes 

 free from the proboscis, it bends a little backwards and upwards, 

 running along the lower surface of this organ for a short distance ; 

 then, having undergone a flexion in the opposite direction, it 

 directs itself a little to the left to terminate in the slightly elon- 

 gated portion of the stomach (fig. 12 n). It is extremely difficult 

 to follow the early phases of the development of the oesophagus ; 

 for it is surrounded by the proboscis, whose parietes are both 

 thicker and more opake than its own ; in some places it is en- 

 tirely covered by it. It is for this reason, that we have been un- 

 able to determine if the oesophagus is formed, at once, in all its 

 length, or if a portion appears at first, and elongates until it be- 

 comes united with the stomach. The latter organ is found a 

 little to the left, and, at first, is almost spherical. It appears 

 to arise thus : a grayish semitransparent mass exudes from a 

 single yelk, soon becoming invested by a delicate pellicle, which 

 completely encloses this same yelk (fig. 9 m). This membrane 

 at first stretches upwards to become united with the oesophagus, 

 and afterwards downwards to give rise to the intestine, which 

 turns towards the right side of the body (fig. 11 o). It is by 

 reason of this origin that we see the stomach always filled, so to 

 speak, with yelk-granules, which are constantly agitated by the 

 vibrating cilia with which the parietes of the stomach are pro- 

 vided. These cilia are found, not only on the internal surface of 

 the latter organ, but W'e have also observed them in the oesophagus 

 and in some parts of the intestine. As we have been unable to 

 follow the intestine for more than a small portion of its course 

 (fig. ] 1 e), we have not made out the anus. 



It is at this period that the first outlines of the nervous system 

 are distinguishable: they are tv\'o compact, ovoid and yellow 

 bodies (cerebroid ganglia), which surround the oesophagus ; and 

 about the same time, the rudiments of the two pedal ganglia, 

 placed side by side, having a strong yellow hue and more or 

 less ovoid in form, make their appearance. 



