123] COMPARATIVE STUDIES ON NEMATODES— HETHERINGTON 19 



material in moist surroundings; bilaterally symmetrical; mouth subtermi- 

 nal, ventral, limited by three lips, one dorsal and two subventral; tails 

 acutely conical, presenting three caudal glands which open at its point. 

 Cuticula smooth, covered by scattered sensory papillae; epidermis of dis- 

 tinct cells; four bands, dorsal, ventral and laterals, separating four muscular 

 fields; muscle cells of large size, few in number; lateral bands present- 

 ing scattered unicellular cutaneous glands. 



"Buccal cavity tubuliform, short; anterior intestine (esophagus) 

 elongated with tripartite lumen, lined interiorly by a cuticular membrane, 

 differentiated into a clubshaped esophagus swollen at its terminal portion 

 and a bulb with valves (proventricle); middle intestine of entodermal 

 origin, formed of a small number of large cells, giving forth sometimes a 

 dorsal cecum in its anterior region; terminal intestine short, lined by a 

 cuticular membrane in connection at its origin with three unicellular rectal 

 glands. Excretory apparatus paired, comprising on each side of the body 

 an anterior canal and a posterior canal which come to open by a 

 lateral pore where there also empties a unicellular gland. Sometimes this 

 apparatus is double and admits of a second system of canals opening in the 

 posterior half of the body. (This form is realized in some females of the 

 genus Rhabditis opening alone without any single gland by a small pore 

 laterally situated in a band of muscles.) 



"Sexes separated; sexual dimorphism faint, the male being character- 

 ized simply by a richer development of papillae in the presence of the 

 sexual orifice. Genital glands paired; the two genital tubes of the male 

 being differentiated into testicle, vas deferens and ejaculatory canal 

 opening a short distance in front of the anus and extending in parallel 

 toward the anterior portion of the body; two cement glands empty 

 into the proximal region of the ejaculatory canal; copulatory organs 

 represented by two equal spicules sliding in an unpaired groove (guberna- 

 culum). The female apparatus is formed of two tubes differentiated into 

 ovary, oviduct, uterus and vagina, opening anterior to the middle of the 

 body and extending in parallel course toward the front; ovaries clublike, 

 oocytes not very numerous; uterus serving for storage of a very small 

 number of large sized eggs, borne only to a slight stage of development. 

 The number of genital tubes may advance sometimes to two or even three 

 pairs. 



"Eggs homo-lecithal, with clear cytoplasm; segmentation total, 

 unequal. The larva leads a free existence comparable to that of the adult 

 and undergoes four moults in the course of its evolution or growth, its 

 principal increase in size occurring at the moments of these moults, (a 

 character conserved in Cepkalobus ciliatus). The genital organ is repre- 

 sented in the hatching larva as an unpaired group of two germinative cells 

 and of two somatic cells; this group which remains unpaired throughout 



