TEICHOPLAX, THE DlCYEMJD^ AND ORTUONEGTID^l. 67 



The other female (Fig. 32, C] is, on the contrary, ovoitl, flat- 

 tened, and unsegmented, being ciliated all over ; it differs 

 furthermore from the elongated female in possessing on one 

 side near the anterior 'extremity a granular mass containing a 

 large nucleus whose significance is entirely problematical. 



Associated with the difference of form of the two females 

 there is a difference of function. In the elongated form when 

 the ova are mature the anterior two segments split off as a 

 cap and allow the ova to escape, and, on fertilization, these 

 give rise to males. In the ovoid form, however, the ova are 

 imbedded in a gelatinous mass, and are liberated by the 

 breaking up of the parent into a number of fragments ; from 

 the ova females of both forms develop. 



The systematic position and affinities of the Dicyemidae and Orthonec- 

 titla- is a matter of uncertainty. They have been held by some authors to 

 possess affinities with the Gregarinida and by others to be degenerate flat 

 worms, while others have sought to trace resemblances to the Rotifers. 

 The granular mass with the large nucleus which occurs in the ovoid 

 Rhop<tliira has been supposed to represent, a rudiment of a digestive tract, 

 while the superficial metamerism of the male and elongate female of the 

 Orthonectida may possibly point to a derivation from more highly organ- 

 ized ancestral forms. There can be but little doubt that the Dicyeraidse and 

 Orthonectida are closely related, but at present sufficient evidence is want- 

 ing to warrant any definite conclusions as to their relationships to other 

 forms. 



LITERATURE. 



TRICHOPLAX ADH^ERENS. 



F. E. Schulze Uber Trichoplax adharens. Abhandl. Akad. Wiss. Berlin, 

 1891 (see also Zoolog. Anzeiger, vr. 1883). 



DICYEMIDAE. 



C. 0. Whitman. A Contribution to the Embryology, Life-history, and Classi- 

 fication of the Dicyemids. Mitth. a. d. Zool. Station zu Neapel, iv. 1882. 



ORTHONECTIDA. 



C. Julin. Contributions d Vhistoire des Mesozoaires. Archives de Biologie in 



1882. 



