The process of diminution is not confined to the 

 nematodes. Members of the Diptera (Miastor), Coleop- 

 tera (Dytiscus and Colymbetes), and Lepidoptera 

 (Lymantria, Orgyra, Phragmatobia, Ephestia, Philosamia, 

 etc.) also show a similar phenomenon. In the nematodes 

 the process always ac;ompanies the localization of the 

 germinal "stem cell" and is confined to those cells which 

 are derived from the "stem cell", but whose descendants 

 become "soma cells". Only the cells which contain the 

 cytoplasmic area destined to become germ cells fail to 

 undergo diminution. Diminution is thus early in somatic 

 history. The same is perhaps true in the case of Miastor, 

 where diminution is confined to the last oogonial divi- 

 sions. It might seem to separate chromatin useful in germ 

 cells, though net in soma cells. In the Coleoptera the 

 process comes late in the germ-line history and does not 

 separate somatic from germinal chromatin. Among the 

 Lepidoptera, diminution occurs after the chromosomes are 

 set free from the nucleus (during metaphase time) and 

 frequently is found only during the maturation divisions 

 of the egg. This variation in the time of occurrence 

 prevents any interpretation of the phenomenon as one 

 of separation of somatic and germinal types of chromatin. 

 The only generally accepted fact common to all cases 

 of diminution is that it is oxychromatin which is lost and 

 basichromatin which is retained. According to Fogg 

 (1930) "The only safe conclusion that now seems ad- 

 missible is that diminution plays no primary or essential 

 part in differentiating the germ-line from the somatic. 

 It is rather a by-product of conditions existing in the 

 cytoplasm which may vary widely in different species in 

 respect to the time of its occurrence, its modus operandi, 

 and its physiological significance". 



Several workers have reported the loss of portions of 

 chromatic material by means other than "diminution." 

 Chief of these methods is through the "cytophore" form- 



ation which accompanies the metamorphosis of the 

 spermatid in many animal groups. This phenomenon has 

 been reported for Cystidicola farionis (Ancyracanthus 

 cystidicolu) (Mulsow, 1912), Toxocara vulpis (Belascaris 

 triquetra) (Marcus, 1906a, Walton, 1918), Parascaris 

 equorum (Hertwig, 1890; Mayer, 1908; Sturdivant, 1934), 

 Ascaris lumbricoides (Hirschler, 1913), Rhabdias bufonis 

 (Boveri, 1911; Schleip, 1911), and Spirina parasitifera 

 (Cobb, 1925, 1928). 



Among the nematodes the two sexes are normally sepa- 

 rate, although a number of hermaphroditic forms are 

 known, particularly among those species which are free- 

 living (Maupas, 1900 Potts, 1910; Cobb, etc.) or those 

 which alternate between free-living and parasitic genera- 

 tions (Boveri, 1911; Schleip, 1911). In such cases the 

 parasitic generation is the one showing hermaphroditism. 

 In many of the bisexual forms the males show an "XO" 

 type of sex chromosome (occasionally an "X" complex) 

 and the females an "XX" condition. A similar condition 

 is known in the hermaphroditic generation of Rhabdias 

 bufonis and in a single unusual specimen of P. equorum 

 var. bivalens (Goulliart, 1932). In both of these cases the 

 spermatozoa are "XO" and the eggs "XX" in type. The 

 formation of the hermaphroditic generation of R. bufonis 

 is probably due to the non-viability of the non "X"-bearing 

 spermatozoon when produced by the free-living males, 

 but in the hermaphroditic generation both types of sperm 

 ("X" and "O") are viable and hence union with the "X"- 

 bearing eggs produces the free-living generation males, 

 "XO", and the females, "XX". The "XY" and "XX" 

 condition is doubtfully reported from several species. The 

 only clear-cut case is one of a multiple "X" and simple 

 "Y", and multiple "XX", from a single species 

 (Contracaecum incurvum = Ascaris ineurva) by Goodrich 

 (1916). In the great majority of nematodes, the hetero- 

 chromosome has not been recognized, possibly because, as 





K 



% 



Fig. 150. 



A. — Toxocara canis; Ilnd. spermatocytes (12 & 18 "dyad" 

 chromosomes; X = 6). B. — Contracaecum incurvum; Anaphase 

 of 1st. spermatocyte (13 + lagging X-group, & 13 + Y ; X = 8, 

 Y = 1). C. — Heteraleis papulosa; Ilnd. spermatocytes (4 fe 5 

 "dyad' chromosomes; X — 1). D. — Beterakis spumoaa; Ilnd. 

 spermatocytes (4 & 6 "tetrad" chromosomes; X = 2). E. — Nema- 

 tospira turgida; Ilnd. spermatocytes (5 6 6 "tetrad" chromosomes; 

 X = 1). F. — Trirhosomoides crassicauda ; Ilnd. spermatocytes (3 

 & 4 "tetrad" chromosomes; X = 1). G. — Toxocara vulpisj Ilnd. 

 spermatocytes (10 & 12 "tetrad" chromosomes; X = 2). H. — 



Cruzia tentarulata ; Ilnd. spermatocytes (5 & 6 "tetrad" chromo- 

 somes; X = 1). I — Contracaecum spiculigerum ; Ilnd. spermato- 

 cytes (7 & 8 "tetrad' chromosomes; X = 1). J. — Mastophorus 

 yniiris : Ilnd. spermatocytes (4 & 5 "dyad" chromosomes; 

 X = IK K. — TOTOcara rati ; Ilnd. spermatocytes (9 & 

 9 "monad" chromosomes ; heterochromosome, X = 1. attached to 

 one autosome). L. — Physaloptera turgida; Ilnd. spermatocytes 

 (4 & 5 "dyad" chromosomes; X = 1). C, after Goodrich, 1916, 

 J. Exper. Zool.. v. 21 ; others original. 



210 



