DEVELOPMENT. 



77 



in Corijmorpha nutans to a laborious examination, wliich has led me to adopt the process 

 now about to be described, as the true interpretation of the phenomena presented in this 

 hydroid. 



We first find that four equidistant processes (woodcut, fig. 31 B c), consisting of cndodcrm 

 and ectoderm, with an included cavity, which is a continuation of that of the hernia-like tubercle just 

 mentioned, have begun to grow upwards from a circle round the summit of this primordial bud. 

 These, however, do not show themselves as free processes ; for simultaneously with their appear- 

 ance the ectoderm of the summit of the bud becomes split into two layers {«', a"), which become 

 more and more widely separated from one another as the processes continue to elongate, the 

 outer layer arching over the space which is surrounded by the four processes. During this 

 elongation the ectodern which occupies the four intervals between the roots of the processes is 

 carried upwards as a continuous membrane, stretching across from one process to another in the 

 manner of a web. 



EiG. 34. 



Development of the Planoblast in Con/morfha nutans. 



A, Very early stage of the medusa-bud when it presents the form of a simple hernia-like tubercle, whose cavity is in com- 

 munication with the somatic cavity of the hydroid; a, ectoderm; I, endoderm. 



B, More advanced stage, a, ectoderm ; b, endoderm ; «', the more external of the two layers, into which the estoderm 

 of the bud has split; a", the more internal of these two layers; c, commencement of radiating canals. 



C, Stage still more advanced, a, ectoderm ; b, endoderm ; c, radiating canals ; d, manubrium. 



D, Transverse section of C. a, ectoderm ; b, endoderm ; c, radiating canals ; d, manubrium. 



E, A stage still more advanced than C. The distal ends of the radiating canals have become dilated into bulb-like expan- 

 sions, one of which has begun to extend itself as a marginal tentacle. 



F, Transverse section of E. 



G, A stage somewhat more advanced than E. The bulbous terminations of the radiating canals have coalesced, and one 

 of them has become projected into a thick tentacle. 



H, Medusa, just after liberation from the trophosome. 



The result of this is, that we have now the distal portion of the bud in the form of a deep 

 cup, closed over by a layer of ectoderm, and having its walls traversed by four equidistant csecal 



