DEVELOPMENT OP AMPHIURA SQUAMATA. 149 



Prouho (15) finds the genital rachis arises as a bud close to 

 but independently of the pseudo-heart. Its further history is 

 similar to that in Ophiurids. I think his statement of the 

 independent origin of the rachis and ovoid gland requires con- 

 firmation. Russo (17) has made the strange error of saying 

 that it results from Ludwig's and Hamann's researches that 

 the genital organs, like the genital bursse, are of ectodermic 

 origin. 



Summary and General Conclusions. 



The most important results detailed in this paper are as 

 follows : 



1. The primitive germinal cells are peritoneal. 



2. The ovoid gland is a solid organ^ which develops 

 from a portion of the rudiment which gives rise to the 

 primitive germinal cells. 



3. The axial and aboral sinuses are involutions of 

 the coelom, and have no connection with the ampulla 

 of the stone canal or each other. 



4. The genital rachis is an outgrowth from the 

 ovoid gland into the aboral sinusj the formation of 

 sinus and rachis proceeding together. 



5. There is no evidence of the existence of Lud- 

 wig's haemal system in Amphiura squamata. 



6. Both kinds of cells, germinal and interstitial, 

 which are found in the genital rachis, are formed in 

 the ovoid gland. 



7. The germinal cells are formed from peritoneal 

 cells directly; there is no evidence of the transforma- 

 tion of the special cells of the ovoid gland into 

 Urkei mzellen. 



The conclusions which I draw are these : that Echinoderms 

 agree with other Coelomata in the origin of their genital cells. 

 These latter have at first an unsymmetrical position in Echi- 

 noderms, and afterwards take on a radially symmetrical dis- 

 position in correspondence with the secondarily acquired 

 radial form of the body. The origin of these cells adjacent 



VOL. XXXIV, PART II. NEW SBR. L 



