DEVELOPMENT OF PARAVORTEX GEMELLIPARA 455 



vesicle, and connected with the atrium by a slender duct of 

 a length about equal to its own diameter. This canal as de- 

 scribed by von Graff for Graffilla buccinicola is shorter but none 

 the less definite. It is therefore characteristic of the genus 

 Graffilla that the seminal receptacle is not sessile upon the atrium 

 but connected with it by a canal. An examination o ' the 

 Turbellarian discovered by Linton reveals no such reservoir. 

 This American species may be described as a Vorticid Rhab- 

 docoele occasionally reaching 2 mm. in length and 0.80 mm. in 

 diameter at its widest part; elongated ovoid in form while at 

 rest, young specimens nearly linear when moving rapidly, pos- 

 terior half of body somewhat broader, anterior quarter more 

 flattened than central and posterior portion which is nearly 

 cylindrical; ends blimtly pointed, the posterior often being the 

 more acute; white with yellowish tinge, semi-transparent; 

 body contractile and extremely flexible; crawls on bottom some- 

 times in a straight line, often performing circus movements; 

 sometimes swims freely in water, revolving about its longitudinal 

 axis and so follows a spiral course; pharynx sub-globose (dolii- 

 form) opening anteriorly into a small vestibule leading to the 

 mouth; the latter is ventral but so close to the anterior end that 

 it is directed forward; oesophagus not distinct from the spindle- 

 shaped intestine into which it merges; intestine extends nearly 

 to the posterior end, lies in upper half of body, walls thick, 

 composed of large cells elongated toward the lumen; two black 

 reniform eyes above the pharynx and anterior to the well devel- 

 oped two-lobed brain. Genital pore ventral at the end of the 

 anterior third of the body, opening into a large atrium; promi- 

 nent pear-shaped seminal vesicle carries at its lower end a mus- 

 cular penis (without chitinous parts) which lies in a very small 

 atrium masculinum; atrium produced posteriorly and dorsally 

 into a pouch which acts as a bursa copulatrix; distensible an- 

 trum femininiun extends posteriorly from the middle of the 

 posterior wall of the atrium; antrum indistinctly forked at its 

 posterior end to form two rudimentary oviducts, but usually 

 so distended with spermatozoa (thus acting as bursa seminalis) 

 that no forking is evident; two large horn-shaped ovaries ^one 



