102 F. H. STEWAET. 



Platylielmia^ NenicrtineSj Rotifers, Cliastopods, and embryonic 

 Mollusca." 



In all text-books the Nematodes are placed in a very 

 isolated position, and no attempt is made to compare them 

 with other groups. This, I believe, is largely due to tlie 

 fact that most Avork lias been done on parasitic forms, and 

 that these have been held up as the types of the group. But 

 even although the great majority of a group were parasitic, 

 it is to the free-living minority we should go for the type, 

 and not to the secondarily modified majority. 



I therefore selected for study a free form Oncholaimus 

 vulgaris (Bast.), a parasitic form Ascaris clavata (Rud.) 

 to compare with it, and an embryo of a parasite to connect 

 the two, if possible. 



No member of the genus Oncholaimus has been investi- 

 gated by modern methods. I therefore have gone thoroughly 

 into its anatomy. 



In regard to A. clavata the alimentary and excretory 

 systems have been fully described by Jiigerskiold (9). I have, 

 therefore, limited my work to the reproductive system, while 

 in the embryo I have confined myself to the excretory organs. 



The specimens were all obtained at St. Andrews, and a 

 large part of the practical work was done at the Gatty 

 Marine Laboratory there. My thanks are due to Professor 

 Mcintosh for the use of the laboratory and for his kind 

 assistance in many other respects. 



Oncholaimus Vulgaris (Bast.)^ 



Measurements : 



Male . . Length . 10—15 mm. 



,, . . Breadth (max.) 135 — "221 mm. 



Female . Length . 12 — 15 mm. 



„ . Breadth . "18 — '225 mm. 



Tiie body is elongated and cylindrical, tapering very 

 slightly and slowly to the anterior extremity (PI. 7, figs. 1 



* Bastiau (2). 



