Chilton. — On Cercaria in the Cockle. 323 



species in the character and arrangement of the setae on the tail, 

 and I propose to give it the name Cercaria pectinata. 



Cercaria pectinata, n. sp. Plate XIX. 



Similar to C. villoti, Monticelli (= C. setifera, Villot), but with 

 the " setae " arranged in two rows along the sides of the tail, 

 instead of forming rings around it ; each " seta " consisting of 

 a short vertical row of long bristles. 



Hab. In Chione stutchburyi, Otago Harbour. 



General Notes. 



The sporocysts (fig. 1) were numerous in each cockle in which 

 they were found, particularly in the first one, in which there 

 must have been several hundreds. They were lying external to 

 the body in the spaces between the mantle-lobes, the gills, &c. 

 Each sporocyst is about 4 mm. long and 075 mm. broad, sausage- 

 shaped, but somewhat narrowed at each end, both ends being 

 alike. By alternate contractions and expansions they were 

 capable of creeping about somewhat slowly with a worm-like 

 motion. The whole of the interior of each sporocyst was in 

 nearly all cases filled with fully developed Cercarice just ready 

 to escape, and through the semi-transparent walls of the sporo- 

 cysts these Cercaria^ could be seen often moving about within. 

 The number of Cercarice in each sporocyst varies to some extent, 

 but usually there were a dozen or more. Swimming among the 

 sporocysts were numerous Cercarice that had already escaped, 

 and if a sporocyst were artificially ruptured the contained Cer- 

 carice at once began to swim freely about. In a few cases the 

 Cercarice were seen escaping naturally through the walls of the 

 sporocyst, and in these cases they made their way through the 

 lateral wall and were apparently able to penetrate this at prac- 

 tically any point. 



Occasionally the sporocysts contained, besides fully de- 

 veloped Cercarice, one or two rounded or elongated masses of 

 cells, presumably immature Cercaria?, but in most of the cases 

 observed they contained nothing but fully developed Cercarice. 



The Cercaria (fig. 2) has a long powerful tail nearly twice as 

 Ions as the head ; this tail sometimes showed numerous fine 

 transverse lines or stria?, most evident anteriorly, but these were 

 not made out in all cases. Along each side of the tail is a series 

 of " setae," and by the rapid vibrating action of the tail, com- 

 bined with the use of these " setae " as fins, the Cercaria is able 

 to swim rapidly through the water. When viewed from above 

 during life each " seta " (see fig. 3) appears to be simple, but 

 closer observation shows that each is made up of a number of 

 fine long bristles arranged in a short vertical row and united 

 together at the base so as to form a comb-like structure, the 



