558 Chas. W. Hargitt 



the proximal ])ortioDS seem to constrict to form the pedicel of the 

 i;()noi)hore. Somewhat later the coustrictiou euts off the gonophore 

 from direct communication with the enteron of the stem, as showii 

 in Fig. 0. Coiucident with these changes there appear at the distal 

 end of the organ, whicli up to this time has been simply a typical 

 two-lavered sporosac, a proliferatiou of eetoderm cells, the disso- 

 lution of the middle lamella and the ingrowth of the ectodermio 

 pliig to form the so-called bell-nucleus (Glockenkern), as sho^Yn in 

 Fig. 4. The presence of numerons karvokinetic figures, as well as 

 the micro-chemical reactions of the cells betoken the intense activity 

 of the growing tissue. At first the bell-nncleus is rather globular 

 in form. Verv soou, however, it assumes an oval outline and con- 

 tinues to flatten and extend laterally in ali directions. With this 

 fiattening of the structure there is reestablished the supporting la- 

 mella, a layer of entoderm is formed between it and the bell-nucleus, 

 so that the latter comes to lie between the outer layer and the 

 inner which contains the eggs. Coincident with this development 

 and graduai extension of the bell-nucleus there has been a diffe- 

 rentiation of its cells. Along its entire inner surface there has been 

 differentiated a single layer of cells, forming in section a delicate 

 chain-like series extending the entire length of tlie growing band, 

 as shown in Fig. 5. 



This growth and differentiation continues, gradually extending 

 US a delicate sheet, laterally and proximally, the inner chain-like 

 series forming an extremely delicate ectoderma! membrane over the 

 outer cgg layer, the other layer of ectoderm forming the lining of 

 the sub-umbrella of the medusa and overlying the thin layer of 

 entoderm, to which referenee was made above. This process con- 

 tinues tili about half of the interior cavity of the gonophore is thus 

 supplied witli a double layer of ectoderm, one covering the eggs. 

 which in the mean time bave become somewhat evenly distributed 

 over the develo})iug manubrium, the other constituting the lining of 

 the beli, as just mentioned, and as shown somewhat diagrammati- 

 cally in Fig. 7. 



With the completion of this ectodermic investment there occurs, 

 apjìarcntly, both an expansion of the lateral walls of the gonophore 

 to approximately the sliape of the future medusa, and also a con- 

 traction of the cntodermic walls into a more nearly cylindrical and 

 conical shape, thus giving rise to the manubrium already referred 

 to. This contraction to forni the manubrium is apparcntly a purely 



