428 ON D1DYMORCHIS, 



where the short wide duct runs backwards from it, open the two 

 vitelline ducts. The vitelline glands are a pair of narrow, irregu- 

 larly lobed bodies which extend on either side between the 

 intestine and the lateral border. There is no bursa copulatrix. 



The eggs were found attached separately to the epipodites of 

 the Crayfish. Each is enclosed in a chitinoid shell, having a 

 slender pencil-like process projecting from it. Before it is hatched 

 the young animal has completely assumed the characteristics of 

 the adult, except that the reproductive organs are not yet 

 developed. 



The Rhabdocoele above described apparently approaches on 

 the whole nearer to the Vorticida than to any of the other known 

 groups. The form of the pharynx is essentially the same, and 

 the general arrangement of the reproductive apparatus corresponds 

 fairly closely. Perhaps also there may be some resemblance with 

 regard to the excretory system, since in the genus Vortex the 

 vessels seem to open on the exterior in the neighbourhood of the 

 pharynx. 



In the reproductive system the chief difference, in addition to 

 the posterior position of the testes and the peculiar form of the 

 penis, seems to consist in the absence of a bursa copulatrix. The 

 integument of the Vorticida also appears to differ from that of 

 the new form, the epidermis in that family assuming the form 

 of a cylindrical epithelium; while in Didymorchis it is a thin 

 protoplasmic layer with nuclei at wide intervals : and in the 

 Vorticida the unicellular glands secreting rod-like bodies apj)ear 

 to be absent. 



Von Graff's definition of the Vorticida is : — " Rhabducoeler 

 mit einer Greschlechtsoffnung, mit Keimdotterstocken oder getrenn- 

 ten Keim- und Dotterstocken, mit weiblichen Hulfsapparaten, 

 stets einfachem Uterus und compacten paarigen Hoden : Mund- 

 offnung bauchstandig und in der Regel nahe deiri Vorderende, 

 Pharynx (mit 1 Ausnahme) ein Pharynx doliiformis. Das 

 chitinose Copulationsorgan sehr mannigfaltig."* 



* " Monographie der Tuibellarien i. Rhabdocoelider," p. 205. 



