40 FOSSIL MEDUSA. 



Dr. Robert P. Bigelow on the development of Cassiopea xamachana. 1 He 

 states that it exhibited a phase of budding- and fission that might aid in the 

 better understanding of the fossil forms. I wrote to Dr. Bigelow, and he 

 very kindly sent me his notes and original drawings for examination. 

 These show that in the scyphostoma larvae the process of budding is carried 

 on by the formation of a swelling on one side of the calyx just above 

 where it tapers into the stem. The swelling increases in size, becoming 

 hemispherical and then elongating. As it elongates a constriction appears 

 close to the body of the scyphostoma; the constriction deepens as the bud 

 alters its shape, so as to cut off the lumen of the bud from the digestive 

 cavity of the scyphostoma, leaving a pear-shaped body attached to the 

 scyphostoma by a very slender neck of jelly covered by the ectoderm. 

 Sometimes a second bud starts in exactly the same place as the first before 

 the latter drops off. As soon as it is free the bud becomes a planula-like, 

 free, swimming larva. The point of interest in relation to the growth and 

 subsequent dropping off of the bud is the fission-like process by which it 

 secures its freedom from the parent larva. It is not fission in the sense of 

 fission in Gastroblasta raffaeli, but it is suggestive of a type of fission that 

 may be represented in Cambrian medusas by the growth and cutting off of 

 portions of the body of the medusa, as illustrated by Laotira cambria. 



In speaking of fission among the hydroids, Dr. Allman states that, 

 while budding constitutes a highly characteristic and all but universal 

 phenomenon among the Hydroida, multiplication by spontaneous fission 

 occurs, although it is rare and exceptional. He mentions an instance 

 described by Kolliker, and describes one that came under his own imme- 

 diate observation. It occurred in a campanularian hydroid, Schizocladium 

 ramosum. 2 Stating the peculiarities of the species, he says that it is a pro- 

 fusely branched form, and that besides the ramuli which support the 

 hydranths, others are developed in abundance from all parts of the hydro- 

 caulus. These commence just like the ordinary ramuli, as offshoots from 

 the hydrocaulus, and consist as usual of a continuation of the ccenosarc 

 by a chitinous perisarc. Unlike the ordinary branchlets, however, they 

 never carry a hydranth. After the entire ramulus has attained some length 



1 Professor Brooks thinks that this species may be identical with the Cassiopea frontlosa which 

 was somewhat imperfectly described by Agassiz. 



-A Monograph of the Gymuoblastic or Tnbularian Hydroids, by George James Allmau (a publi- 

 cation of the Ray Society), Part I, 1871, p. 151. 



