(spermules). In Spirina parasitifera* each spermatid 

 eventually gives rise to one hundred and twenty-eight 

 spermatozoa, the final differentiation occurring only 

 after the spermatogenous tissue reaches the oviducts of 

 the female. Certain arachnids (Warren, 1930), which 

 produce two to four spermatozoa from each spermatid, 

 show an approach to this condition. A somewhat similar 

 phenomenon is also reported from certain snails. 



In the female a similar program is followed to a great 

 extent, except that the meiotic divisions frequently occur 

 only after the spermatozoon has entered the primary 

 oocyte (Boveri 1887; Sala, 1895; and modern observers). 

 The spindle of the first meiotic division is always ec- 

 centric in position and the resultant cells are extremely 

 unequal as to cytoplasmic content. The first polar body 

 is separated from the large secondary oocyte by this 

 division. The second division similarly forms a single 

 large functional ovum and a second small polar cell. 

 The first polar body occasionally divides into two equal 

 cells. None of the polar cells are functional as far as 

 is known among nematodes, although cases of entrance 

 of the sperm into such cells have been noted. 



As stated above, the significance of meiosis lies in the 

 reduction to n/2 of the chromosomes which have under- 

 gone synapsis during the formation of bivalent chromo- 

 somes (homologous pairs). This synapsis is now regarded 

 as being always "side by side" (para-synapsis) among 

 the nematodes. If such members of homologous pairs 

 are compound chromosomes, their synapsis may give rise 

 to four-parted bivalents during the prophase of the first 

 meiotic division. This occurs during the growth period 

 following the last gonial division of each germ cell of 

 either sex. These bivalents are separated during one of 

 the two following divisions and hence that division is 

 reductional since it separates (disjunction process) hom- 

 ologous structures. The other division, being equational, 

 means that the four resulting nuclei each have a haploid 

 set made up of one chromosome of each kind. In many 

 nematodes the prophase chromosomes of the first divi- 

 sion show both the plane of synapsis and that of a future 

 longitudinal splitting, making "tetrad" chromosomes (if 

 the chromosomes are compound they may thus form 

 "di-tetrads", or, as in Spirina parasitifera, they may 

 form 56-parted bodies). When the first division separates 

 homologous pairs, it is termed "prereductional"; when 

 it is the second division which causes disjunction, the 

 process is termed "postreductional". Most nematodes 

 show "prereduction". If the original bivalent chromo- 

 somes were "tetrads" the resultant chromosomes are 

 "monads"; if "di-tetrads", they become "dyads" in the 

 mature germ cells and in the polar cells. 



During the formation of the prophase chromosomes the 

 stages known as leptotene, zygotene, pachytene, diplotene 

 and strepsitene are poorly differentiated except possibly 

 in the races of Parascaris equorum (Van Beneden, 1887; 

 Boveri, 1888; Griggs, 1906; Bonnevie, 1908, 1912); in 

 most cases the chromosomes behave as quite solid units 

 derived in a very early stage from a segmented spireme 

 thread (Vejdovsky, 1912; Walton, 1918, 1924; Sturdivant, 

 1934). 



During the process of spermatogenesis extra-nuclear 

 bodies such as the centrioles (?), chondriosomes (Meves, 

 1911; Held, 1912, 1916; Hirschler, 1913; Romeis, 1912 

 Sturdivant, 1931, 1934), "yolk granules" (Sturdivant, 

 1934; Wildman, 1912; Walton, 1916a), and Golgi 

 bodies (Sturdivant, 1934) are more or less evenly 

 distributed so that each spermatid receives its comple- 

 ment of each of these elements in addition to the haploid 

 number of chromosomes. The "yolk granules" are thought 

 to be largely composed of glycogen and to be low in 

 protein and lipoids (Kemnitz, 1913), although Bowen 

 (1925) believes that further analyses are needed. These 

 "yolk granules", or refringent globules, are apparently 

 derived through the activity of the Golgi bodies, and 

 therefore are pro-acrosomal in nature. The contained 

 bodies in the center of each globule disappear during the 

 spermatid metamorphosis and are perhaps to be regarded 

 as temporary indications of precocious acrosomal gran- 

 ules, structures quite characteristic of insect spermatozoa 

 (Sturdivant, 1934). They are not mitochondrial in nature 



•Chitwood has re-examined this form and reports that the above 

 observation was bas3d on a misinterpretation of the structures 

 present. (see page 125 for his explanation). 



as earlier reported. The refringent globules eventually 

 fuse to form the "refringent body" of the mature sperm- 

 atozoon, which thus contains a structure homologous 

 with the acrosome of other types of spermatozoa (Bowen, 

 1925). The Golgi remnants are cast off during the cyto- 

 plasmic reduction and cytophore formation of the maturing 

 spermatid (Sturdivant, 1934). 



The spermatozoa of nematodes are described as non- 

 flagellated, frequently amoeboid cells, containing a con- 

 siderable amount of stored material in the "refringent 

 body", or acrosome. This type of spermatozoon is usually 

 regarded as a simple modification of the fundamental 

 structural plan of a flagellate sperm and has arisen 

 secondarily during the evolution of this phylum. The 

 fact that the acrosome is not always at the morphologic- 

 ally anterior end of the spermatozoon is not of particular 

 significance. Certain of the acrosomal bodies are hollow 

 (Nemotospira turgida) , and this may very doubtfully 

 represent the position of an axial tail filament in this 

 pseudo-flagellate form. No other evidence concerning any 

 axial filament is apparently available for the nematodes. 

 Passalurus ambiguus (Oxyuris ambigua) has spermatozoa 

 that may almost be considered as flagellate (Meves, 1911; 

 Bowen, 1925). Recently Chitwood (1931) has described 

 the spermatozoa from Trilobus longus which seem to be 

 of truly flagellate form. This is to be expected since 

 Trilobus is very close to the hypothetical ancestral nema- 

 tode form which is believed to have possessed a 

 typically flagellate type of sperm. Passalurus (Oxyuris) 

 and Trilobus have the acrosomal body at the morphologic- 



Fig. 147. 



Nemic spermatozoa. A. — Parascaris equorum; B. — Passalurus 

 ambiguus; C. — Antiroma pellucida ; D. — A. eberthi ; E. — Tricho- 

 somoules crassicauda; F. — Tetradonema plicans; G. — Trilobus long- 

 us; H. — Dorylaimopsis metatypicus ; I-L. — Rhabditls strongyloides 

 (I. J, L. ameboid stage, various views; K, resting stage) ; M. — 

 Paracanthonchus viviparus; N'. — Halichoanolaimus robustus ; O. — 

 Tripyla papillata; P. — Axonolaimus spinosus. B, after Meves. 1920, 

 Arch. Mikr. Anat. v.. 94 ; C. after de Man, 1886. Nordsee-Nemato- 

 den. Leipzig; D. after de Man. 1889. Mem. Soc. Zool. France, V. 2; 

 F. after Cobb. 1919, J. Parasit.. v. 5 ; G-P. original, Chitwood ; 

 A, E, original. Walton. 



206 



