DEVELOPMENT OF PARAVORTEX GEMELLIPARA 463 



were removed from eight mussels after the adductors had been 

 cut, and onlj^ a single one when the viscera had been dissected. 

 Considering the numerous crevices between the gills, visceral 

 mass and mantle it seems very improbable that those worms 

 which were not dislodged during the first washing were within 

 the alimentary canal or kidney, but became freed from the 

 mantle cavity in the two subsequent rinsings. The evidence 

 pomts to the latter as being the usual abode of Paravortex 

 gemellipara. 



The number of worms obtained from different lots of mussels 

 varies immensely. Patterson is of the opinion that there is 

 a periodicity in the reproductive activity of this animal, but 

 it is probable that the difficulty which he sometimes found in 

 obtaining specimens was merely due to the irregularity of their 

 occurrence. It has often been observed that one pailful of 

 mussels may yield an abundance of worms, while another col- 

 lected in a few hours and from the same mussel bed may pro- 

 duce very few. The conclusion is that only a portion of the 

 mussels in the bed contam conuuensals. The success in ob- 

 taining specimens, therefore, depends upon the selection of 

 the proper mussels. 



Although usually no accurate count of the number of worms 

 taken from given numbers of molluscs has been kept, a great 

 variation is known to occur in their distribution. In the vicin- 

 ity of New Haven Paravortex is abundant in certain mussel 

 beds and almost entirely wanting in others. Any situation 

 between high and low tide marks seems to be as favorable as 

 another. Not always do those mussels which receive the most 

 sunhght, even in winter, yield the greatest number of worms. 

 In December, beds which were exposed to bleak winds some- 

 times gave better results than others which were fastened to 

 rocks in sheltered coves with southern exposure. 



Although, doubtless on account of increased metabolic activity 

 and hence more prolific reproduction, Paravortex is more abun- 

 dant in warm weather, still specimens may be obtained without 

 difficulty at all seasons. I have collected them during every 

 month of the year. Hallez asserts that P. cardii is as abundant 



