772 CHAKLKS L. BOL'LENGEK. 



different situations of the stinging-cell factories it is necessary 

 to examine the development of the medusa in some detail. 



Until recently the accepted view of the development of the 

 gonophores of the Hydromedusse was based essentially on L. 

 Agassiz's observations on Syncoryne mirabilis, published 

 in 1862 (8). His account of the process was confirmed by 

 Hertwig (9); Weismann (10), and almost all later workers on 

 the same subject, and is essentially that to be found in the 

 majority of modern text-books. The following description of 

 the development of the medusa of Bougainvillea is taken 

 from one of the latter (18), and represents the prevailing ideas 

 on the subject : 



The medusa-bud makes its first appearance as a simple 

 hollow bud formed by the evagination of the two layers of 

 the mother-polyp. Multiplication of the ectodermal cells at 

 the apex results in the production of a lens-shaped mass of 

 small cells which sinks below the level of the superficial 

 ectoderm, pressing the endodermal wall in front of it into 

 the shape of a cup. This mass of ectoderm is called the 

 entocodou (Glockeukern), and a cavity which appears in its 

 interior is the rudiment of the subumbrella cavity. It is 

 followed by an invagination of the superficial ectoderm, the 

 wall between the new cavity thus formed and the subumbrella 

 cavity being the future velum. Grrowtli of this subumbrella 

 cavity results in an approximation of the endodermal walls of 

 the coelenteron, and these ultimately fuse into an endoderm 

 lamella except where the circular and radial canals ai'e to 

 lie. The upgrowth of the manubrium from the floor of the 

 subumbrella cavity, the formation of the tentacles and the 

 perforation of the velum and manubrium complete the 

 formation of the medusa. 



A. Goette (11) has recently made a thorough examination 

 of the development of the gonophores of Podocoryne 

 carnea and a large number of other hydroids, and has 

 published a long and elaborate paper on the subject. As 

 the result of his investigations this author concludes that the 

 cui'rent views on the origin of these structures are quite 



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