NO. 6 CLASSIFICATION OF NEMATODES— FILIPJEV 5 



saprozoic forms, the stain penetrates only through these openings, 

 being chiefly ingested through the mouth, the cuticula being quite 

 impermeable to the stain. We know that the internal fluids of the 

 latter forms are of peculiar chemical and osmotic composition, quite 

 different from their external medium which is sometimes variable. 

 The relations existing in marine nematodes, as well as in other 

 marine animals, are generally regarded as primary ones, and we have 

 no reason to consider them as secondary in the nematodes in general. 



There are several morphological structures leading us to the 

 same conclusions, as, for example, the cervical gland or renette. In 

 free marine forms this appears mostly as a simple skin gland, par- 

 ticipating in the general mosaic of the body epithelium just as do the 

 ordinary epithelial cells. It is more complexly developed in parasites 

 or saprozoic forms, having in its primary form two outgrowths 

 lying before and two behind the cervical pore. In young Ascaris 

 larvae it is a rounded cell only, the outgrowths appearing in its later 

 development. But throughout the parasitic nematodes it is always 

 the same unicellular skin gland as it is in the free-living forms, as 

 was shown 30 years ago by Jagerskiold and Golovin. It probably 

 has a function similar to that of the protonephridia, to which it was 

 compared by Cobb (1890-1891), Steiner (1920), and some others, 

 in that the latter organs also are skin glands of one sort. The 

 nematode excretory apparatus is more primitive than the nephridia. 

 The structure of a comparatively complexly developed organ con- 

 sisting of only one cell (or sometimes of two, which makes no differ- 

 ence in principle) could be considered only as a secondary matter. 

 Its excessive and complex development in saprozoic and parasitic 

 forms is probably correlated with the necessity for an independent 

 osmotic relation to the external medium. 



Another point of comparison is the cell constancy of the parasites, 

 affecting in some instances all their organs except the genitalia (cf. 

 Martini, 1916). In musculature it is known as meromyarity and, 

 since A, Schneider, has been regarded by many scientists as a very 

 important systematic character. I do not consider this character as 

 a primary one ; really it means that there are less cells, but that each 

 cell is more complex. The primitive condition is, of course, an inde- 

 terminate number of cells not highly differentiated. Therefore we 

 could not regard these forms as primitive ones, but merely as 

 neotenic larvae of forms with determinate development. The large 

 parasitic forms could be considered as hypertrophic larvae (cf. 

 Filipjev, 1918, 1927). The full-cell nematodes are found mostly 

 among marine forms. 



