PALfiONTOLOGIC CONTRIBUTIONS 129 



by Schmidt (no. 27) for nearly all Asaphidae. Barrande {op. cit., 

 p. 616) states (translated) : " In passing we mention as an inter- 

 esting fact that in Trinucleus bucklandi the eye pro- 

 tuberances which are very marked and constant in young age and 

 during the whole growth of each individual, disappear when it has 

 completed its development. The- specimens which we know all 

 agree in showing this feature, while all preserve in all growth-stages 

 another ornamental tubercle of about the same size on the apex 

 of the glabella. Oehlert (no. 12, p. 320) also comments on the 

 fact that the " eye tubercles seem to exist concurrently with a 

 third tubercle which occupies the middle of the frontal lobe." 

 Beecher in his well-known paper on the "Structure and Appendages 

 of Trinucleus (no. 2) states that a spot or node has been noticed 

 by many observers in the median line of the glabella of that genus 

 and that although its nature has not been demonstrated, it has been 

 considered an ocellus. 



Reed (no. 23, p. 446) states regarding the lateral eye spots of 

 immature (Cryptolithus) Trinucleus, that the visual function of 

 these tubercules in the larval Trinucleus has never been demon- 

 strated, and no description of lenses or visual surfaces has ever 

 been published, so far as he knows adding that however the general 

 similarity between the eye line and eye' spot of Harpes and these 

 structures in the larval Trinucleus, is in favor of regarding the 

 latter as organs of sight, and winding up by the suggestive remark : 

 " From the resemblance of the tubercle on the glabella to those on 

 the cheeks, we might probably regard it as possessing likewise a 

 visual function." 



After recognizing the constancy of occurrence and corresponding 

 probable functional importance of this tubercle on the glabella, 

 we endeavored to find evidence of its ocular nature. The first 

 effort would naturally be to look for lenses, but it is here to be 

 remembered that the parietal or median eyes of arthropods show 

 a wide range of development. Patten, in his Evolution of the 

 Vertebrates and Their Kin, states (no. 13, p. 125) that in the arth- 

 ropods, we may recognize four types of eyes, namely, paired 

 larval ocelli, parietal eyes, frontal ocelli or Btemmata, and the 

 lateral or compound eyes. The larval ocelli are present in the active 

 larvae of most insects and do not concern us here. The frontal 

 eyes or stemmata are in crustaceans modified into other organs 

 (the frontal organs) and here of no concern. Regarding the 

 parietal eye Patten states :' " In the Crustacea and arachnids, two 

 pairs of ocelli unite to form an unpaired ocellar vesicle, or parietal 

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