MONHYSTRELLA 



203 



Fig. 6. Monhyslrella plec- 

 toides n. subg. n. ep. For some 

 distance in front of the nerve- 

 ring the oesophagus is dis- 

 tinctly though slightly altered. 



A critical review of the Mon- 

 hysteras so far discovered and 

 described will undoubtedly re- 

 sult in the establishment of a 

 number of fairly well defined 

 groups, some of subgeneric 

 rank, some of generic. The 

 divisions may be made on the 

 basis of the anatomy of the 

 male organs as well as on that 

 of the mouth parts. These 

 anatomical differences are the 

 outward expression of differ- 

 ences in food habits, and of 

 special activities due to differ- 

 ences in habitat. The Mon- 

 hysteras constitute a hu_ 

 group, of considerable biologi- 

 cal significance. Some species 

 are specially adapted to stud- 

 ies of problems in genetics. 

 The mode of development of 

 the spermatozoa of certain 

 species is worthy of study. 



Ol A. 



(/it., 

 mui-int. 

 him at. 



nil . . . 

 at tut 



inn or. 

 mam. 



mw mi 

 tty fir 

 it 

 nl 



rim 



lit MONHYSTRELLA subg. nov. 



Subgeneric characters. Has the 

 general form and appearance of 

 Monhystera, but differs in the fol- 

 lowing respects: The pharynx is 

 more elongated, somewhat resem- 

 bling that of Cylindrolaimus, but 

 tapers slightly. The oesophagus 

 is not quite of uniform diameter, 

 in this respect somewhat resem- 

 bling that of Plectus in the ante- 

 rior part, but with all the varia- 

 tions less pronounced, so that, at 

 first glance, the oesophagus seems 

 to be rather uniform in structure 

 from the pharynx backward to the 

 cardiac swelling. There is a 

 rather distinct pyriform cardiac 

 swelling, with clear indications 

 of the presence of glands among 

 its muscular tissues. One or two 

 problematical unicellular organs 

 exist in the lateral fields on each 

 side of the body some distance 

 in front of the anus. Otherwise 

 very much as in Monhystera. 

 Possibly Monhystera bulbifera de 

 Man belongs to this sub-genus. 



6. Monhystrellaplectoidesn. sp. 



1.2 10. 17. '-44. 65. 



i75 274 t76 371 ITT 

 The rather thin, transparent, 

 colorless cuticle is traversed by 

 exceedingly fine transverse striae, 

 resolvable only with high powers 

 under most favorable conditions. 

 The thin-shelled eggs appear to 

 be deposited before segmentation 

 begins. 



Habitat: Sand, Washington 

 filter beds; uncommon. Nemas 

 of the character represented by 

 Monhystrella and Monhystera are 

 largely, if not entirely, vegeta- 

 rian. As a rule they are not 

 abundant in covered slow sand 

 filter beds. On one occasion, 

 however, after a long period of 

 winter use, I found such nemas 

 to be fairly abundant. 



