DEVELOPMENT OF THE MIRACIDIUM OF PARAGONIMUS. 179 



to six weeks, at a temperature of from 26°. 7 to 34°.4 C. Nakahama 

 (1883) reported that the ciliated miraeidium developed in twenty-eight 

 days, at a temperature of 30° C. 



In our own cultivations we have endeavored to record the length of 

 time from the day the sputum was expectorated to (1) the day of the 

 first motile miracidia, (2) the day of the first free swimming miracidia, 

 and (3) the day the last motile miracidia were found in the culture. 



Beferring to the observatioja of Kerbert (1881) of the presence of ova 

 in the uterus of the worm developed to the gastrula stage, and to that 

 of Manson (1882) of ova segmented several times in the sputum, we 

 may say in this connection that in freshly expectorated sputum we have 

 never been able to detect segmentation of the germ-cell. 



We have repeatedly been able to grow the motile miraeidium in fifteen 

 days from the time the sputum was expectorated, but in order to do 

 this, it was essential that the ova be thoroughly sedimented on the day 

 the specimen was obtained • and that the water be promptly changed 

 whenever it became at all clouded. Any delay in the first washing or 

 failure to keep the water clean resulted in a longer period of development, 

 though not necessarily in degeneration. 



All cultivations, although the most favorable conditions Avere complied 

 with, did not develop the motile miraeidium in so short a time, some 

 requiring from twenty to twenty- five days. 



Such variations did not appear to correspond to such slight differences 

 of temperature as occurred in the laboratory at different times of the 

 5''ear. Motile miracidia have developed in fifteen days, while the ther- 

 mometer ranged from 25° to 28° C. ; at other times, with a temperature 

 of from 29° to 31° the development was slower. 



Therefore it is apparent that a difference in temperature does not 

 explain the more rapid development obtained in our cultivations than it 

 did in those of Manson and of Nakahama. From our experience it would 

 appear that a more important factor than temperature within the limits 

 indicated is the prompt and thorough washing of the ova and the cleanli- 

 ness of the water in which they grow. 



We have never found free-swimming miracidia in our cultures in less 

 than twenty-five days from the time the sputum was expectorated, but 

 in from twenty-five to thirty-five days they have frequently been noted. 

 Therefore it is evident that the miracidia require, after they first acquire 

 motility, a considerable period for further development before they are 

 capable of leaving the shell. 



A more striking observation is the length of time motile miracidia may 

 remain in the shell before hatching. While as a rule practically all the 

 shells in a culture thirty days old, contained actively motile miracidiii. 

 active, unhatched organisms would persist in the same culture for one 

 hundred and fifty days, and in one case we found shells containing motile 



