788 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



where they are needed. In young tentacles which are still elon- 

 gating the nematocysts are carried out with the ectoderm as it 

 becomes applied to the tentacle base. But after a certain time the 

 tentacle increases only very slowly in length and additional nettling 

 cells are needed to keep up with the increase in diameter. This 

 migration of nematocysts has been seen and described by Mur- 

 bach." After the capsules have become established, the ectodermal 

 covering becomes modified to form the cnidocil (PI. XXXIV, fig. 

 27). The nerve connection in the cnidocil is developed at an 

 early stage. 



Sexual Organs. 



In minute specimens of the adult gonosome the gonads are fre- 

 quently found in their first stage of development. They appear as 

 outgrowths of the ectodermal covering of the radial canals, at first 

 in the form of a ridge projecting downward from the radial canal 

 into the subumbrella at a point two-fifths of the distance from the 

 top of the bell to the margin. The rudimentary ribbon of gona- 

 dial tissue elongates in both directions from the point at which it 

 started. Text-figure 20 shows the condition in Olindias, in which it 

 is similar at first to that in Gonionema. The gonad thus becomes an 

 elongated ridge of tissue which finally reaches to the extremities of 

 the radial chimiferous tubes, and iuci-eases in depth until it hangs 

 down like a ribbon into the subumbrella. Early in its development 

 the ribbon is somewhat sinuous, and as the medusa attains greater 

 diameter the convolutions become more and more numerous, and 

 farther extended on either side of the radial canal, until ultimately 

 the folds are packed tightly together in a solid band of tissue, 

 which at the time of maturity is extended with sexual elements. 

 The process of formation of the sexual organs is identical in the 

 two sexes; it is impossible to tell Avhether a given individual is 

 male or female until the sexual products begin to mature. 



Summary. 



1. Observations on the development of Gonionema indicate that 

 Haeckel's sharp distinctions between jelly-fishes which he groups in 



"L. MuRBACU, 1894, Beitrage zur Kenntnis der Anatoinie u. Entwick. 

 der Nesselorgane der Hydroiden. Archiv. f. Naturg., 60. 



