the large ascaiids and are most numerous in tlie vicinity of 

 the radial nuclei, but they may also occur in the marginal 

 areas or at considerable distance from the nuclei. They vary 

 in number and appearance. When few are present they tend 

 to take the form of coiled fibers, and when many are present 

 the form of thick flecks; both forms may be seen in a single 

 chromidium. Kulmatycki (1922) found such structures as well 

 as a golgi body in cells of the spicule sheath, thereby eliminat- 

 ing the possibility that the ehromidia are homologues of 

 the golgi body ; he named them ascaridochondria, relating 

 them to mitochondria, chondrosomes, etc. ' ' C'hromidia ' ' occur 

 in marginal areas of Anonchus mirabilis (Fig. 84 D-F), even 

 more spectacularly than in Ascaris. Their significance, today, 

 is unknown. 



Ocelli and Pigment Spots. — The occurrence of pigment 

 masses in the Aphasmidia has been mentioned. That such 

 structures exist, has been known since the time of Bastian. 

 Because of their general appearance they have been widely ac- 

 cepted as photoreceptors despite a total absence of evidence 

 that they are connected with the nervous system. Brownish to 

 red granules may be rather irregularly and generally dis- 

 tributed in the esophageal tissue of such forms as oneholaims. 

 Similar pigmented granules may be slightly more concentrated 

 in the subdorsal marginal areas of forms such as Enoplus and 

 Chromadora. In these forms there is a definite pair of "pig- 

 ment spots" but the pigment also extends posteriorly from 

 the spots and may be present to a considerable extent in the 

 .subventral marginal regions of the esophagus. Rauther (1907) 

 regarded the pigment granules of Enophis and Oncliolaimus 

 as excretory granules and thought they were eliminated through 

 the esophageal glands. We find no evidence of the "refractive 

 granules" in the ducts of the esophageal glands and see no 

 reason to assume they are excretion products. Schulz (1931b) 

 upon finding the spots to be within the esophagus in Enoplus 

 reaffirmed Rauther 's interpretation and differentiated such 

 bodies from true ocelli (with lenses) which he observed in 

 Leptosomatum, Thoracostoma and Pnrnsi/mplocostoma. In the 

 latter type he described the lens as an invagination of the 

 superficial cuticle of the bod.v surrounded by pigment and con- 

 nected with a special ocellus cell. He states that he does not 

 believe the true ocellus is connected in any way with the 

 esophagus. On the contrary, the writers have found the ocelli 

 of Lcptosomafiim clongatum to be completely enclosed within 

 the wall of the esophagus ; the lens seems to be formed from 

 the external covering of the esophagus and no special cell is 

 associated with the ocellus. We must conclude that even in 

 this instance the ocellus is a part of the esophagus. If it is 

 innervated, as one would presume, then the esophago-sympa- 

 thetie nervous system must include also, the "optic nerve." 

 In the Desmoscolecoidea, there is definite evidence that the 

 pigment bodies are outside the esophagus; in this group the 

 posterior part of the esophagus is degenerate and the esopha- 

 geal glands outside the general contour. In Monliystera 

 paluilicnla true ocelli are present; these are likewise situated 

 outside the esophagus. 



There remains one additional case of pigmentation in the 

 cephalic region associated with photoperception. In the gravid 

 female of MermiK svbnigrescens Cobb (1926, 1929) described 

 diffuse reddish pigment anterior to the nerve ring. Such 

 pigment is absent from the head of young females and males, 

 only being found in specimens ready to deposit eggs. Though 

 the exact location of the pigment was not determined, the 

 case is interesting since it supplied the only actual evidence 

 of photoperception in a nematode, for egg laying only takes 

 place in the light, ceasing in darkness. That heat is not the 

 stimulus is indicated by the fact that such "egg laying" 

 females will continue to lay eggs though placed on ice in a 

 dish of water so long as the light continues. 



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98 



