198 ROBERT PAYNE BIGELOW ON 



bilaterally symmetrical to one another. We find all degrees of this doubling in the adult 

 from a double-headed rhopalium 1 to two complete parameres, and the same process may 

 be seen in the forked tentacles frequently found in the larvae (Figs. 14 and 21, x) . With 

 the exception of the forked tentacle and the double-headed rhopalium, these stages of 

 duplication are well represented at ?, w, x, y and z in Fig. 30. 



The radially arranged stripes and spots on the exumbrella, which, with a circular 

 band, form the color pattern described in the next section, vary in number with the 

 rhopalia and marginal lobes. But when two rhopalia are close together there may be 

 only one corresponding rhopalial stripe, and it will then occupy a position intermediate 

 between the two. For example, in the specimen mentioned before as having only ten 

 rhopalia, two of the rhopalia were very close together and there was but one rhopalial 

 stripe corresponding to them. The other rhopalia were evenly spread, except that they 

 were absent from one rather wide section of the circle. The rhopalial stripes, nine in all, 

 were placed in a corresponding manner, and were absent from the corresponding area. 



There is also a wide degree of variation in the extent of fusion between the circular 

 band and the marginal spots. The spots on the velar lobes are usually not fused to the 

 circular band in young specimens, and they frequently remain distinct in adults. It 

 was found, however, that this is more usually true of specimens from the Salt Pond than 

 of those from Port Royal. I thought that I could see, also, correlated differences in the 

 ' sizes of certain of the mouth parts, and I was thus led to inquire if there were a division 

 here of the species into two races. For this purpose Table 2, p. 201, was constructed. 

 From this it will be seen that the specimens from the Salt Pond (var. A) have on the 

 average longer oral arms and shorter vesicles than the ordinary specimens from Port 

 Royal (var. B) , while the stomach is of the same size in the two groups. Whether these 

 slight differences are in any way connected with the probable difference in density of the ' 

 water in the two localities, experiment alone can determine. 



In the third column of this table dimensions are given of some specimens from Port 

 Royal (var. C) that are so different from the rest that they might be regarded as of a 

 distinct species. 4 Suspicion of their being merely sports is aroused, however, by the fact 

 that only two specimens (female) were found living among a large number of the 

 usual form. 



The most striking peculiarity of these two specimens was the great number (forty 

 to fifty) of uniformly large oral vesicles, two to four centimeters in length, scattered over 



1 Fewkes, ('82) has observed similar double-headed rhopalia, and it is on account of the variability of the marginal 

 structures that he regards Polyclonia as merely an abnormal Cassiopea. 



1 It is possible that this variety may be the same as Cassiopea frondosa Lamarck of Fewkes, although his figures do not 

 show any large vesicles on the proximal parts of the oral arms. 



