228 liOliEKT PAYNE BIGELOW ON 



SUMMAUY AND CONCLUSIONS. 



Cassiopea iuul Polyciloiiia arc ^'Oiicra ot ilii/.ostoiiiMtoiis mciinsac ])eciiliar]\' inodilicd in 

 adaptation to a sedentary mode of lite in shallow water .hikiuu- the maniiioves honlering 

 ti'opical seas. A c^oinjiarison of specimens of I'dIiii-Iokki /'m/it/osti Au. with Cussiopea 

 xamaclidiiii shows tliat these two forms ai'c specilicMlly distinct, althouuh in general 

 appearance they are very similar and they have the same geographical range and 

 habitat. 



C. vdhiiii'hditd is remarkable for its variability. This is especially shown in the 

 appendages to the month parts and in the strnctni-cs ,it the margin of the undirella. It 

 will be noticed that the most frequent number of rhopalia, in the twent3--seven .specimens 

 examined, was sixteen, Avhich is the typical number for the genus. But the variations are 

 not arranged symmetrically on the two sides of this mode, for specimens having a 

 greater number of rhopalia are more than twice as many as those having less. The 

 species shows a strong tendency toward duplication of the rhopalia and associated strnc- 

 tvu'es of the umbrella; and at the same time the symmetrical relations of the ])arts tend 

 to be preserved. The great majority of scyphonjednsac have only eight rhopalia. and in 

 Cassiopea with its sixteen rhopalia we have a benutifid illustration of Darwin's law that 

 "Apart developed in any species in an extraordinary ilegree or manner, in comparison 

 with the same part in allied species, tends to be highly variable." Study of the color 

 markings and measurements of the'mouth parts indicntes the divisi(ni of the s])ecies into 

 three varieties; and it was in one of these, var. ^1, that the dn|ilication of marginal organs 

 was especially prevalent. 



The color of both larvae and adults is due to a grent extent to the ]iresence in the 

 mesogloea of minute symbiotic algae. That these are phint cells was demonstrated by 

 micro-chemical tests. Their presence undoubtedly enables the nieilnsae to live in water 

 that would be too poor in oxygen for most m.irine animals. 



The search for develo])ing eggs proved nnsuccessfnl. but scyphistoma l.iixae were 

 abundant, and it was found that they were multiplying lapidly by budding. 



The bud arises as an evagination of the body wall of the scyphistoma. There is no 

 evidence of any special gemminal epitheliiun. The bud. when set free, differs from a 

 planula chiefly in the possession of a well-deiined mesogloea and four septal muscles. The 

 septal muscles are showm to be formed as branches of tlu> two adjacent septal muscles of 

 the parent. The mouth of the young scyphistom;i is birnied by a minute perforMtion at 

 the former point of attachment, while the distal end of the i)ud becomes the stem. This 

 remarkable orientation agrees with what Goette and Cl.ius b.ive found in Cotylorhi/a. In 



