F. R. Cotoper Reed — Blind Trihhites. 445 



forms it persists to an adult condition. In the later and higher 

 genera of the Olenidse {Sao and Triarthrtis) in which it occurs 

 it appears at an earlier larval stage owing to acceleration of 

 development, and in Sao it persists throughout life. It is, however, 

 entirely absent from every stage of all later and higher genera which 

 have been studied. 



It is interesting to find an eye-line present in some of the 

 Oonocoryphidge, which are all devoid of eyes and are of a more 

 primitive type than the Olenidee, though in many respects allied to 

 them. We are only acquainted with the later larval stages of some 

 of the Conocoryphid^,' and in these it is. present. It is certainly an 

 archaic feature, for it is characteristic of the Cambrian genera of 

 trilobites, and four-fifths of them are said to possess it, but in later 

 and higher genera it is absent, with the exception of the Olenidse 

 above mentioned. But from the fact that in the Olenidae it makes 

 its appearance on the dorsal shield earlier than the compound eyes 

 on the free cheeks, and that it is also present in larval and adult 

 stages of the more primitive Conocoryphid^ which possess no com- 

 pound eyes, it cannot be maintained that its presence is consequent 

 on the development of eyes or indicates their former existence. 

 Moreover, from its absence in the earliest larval stages of simpler 

 forms and in the least modified members of the Hypoparia, it 

 seems likely to prove to be a secondary and superinduced structure, 

 and not characteristic of the earliest and simplest stages in the 

 phylogeny of the group. With regard to the supposed homology 

 of the eye-line in the Olenidse and Conocoryphidge with the eye- 

 line in the Harpedidee and larval Trinucleiis we have not sufficient 

 evidence to draw any definite conclusion ; but from the fact that 

 in the highest forms (the Olenidse) in which the eye-line is found 

 it runs direct to the palpebral lobe of the compound eye and ends 

 at the facial suture, while in the Conocoryphidee it generally ends 

 short of the facial suture, and branches out into a ramifying 

 network of veins suggesting nerves (e.g. Carausia), and that in 

 the Harpedidae the eye-spot is situated upon it, though not always 

 at its outer termination, it appears probable that this line indicates 

 the course of a nerve or nerve-plexus along which organs of vision 

 in some cases are developed. That its association with eye-spots and 

 compound eyes is more or less accidental and temporary, and is 

 not intimately bound up with its existence, is suggested — (1) hj its 

 absence in all the higher and later genera with the best developed 

 compound eyes ; (2) by its larval appearance before any organs of 

 vision are developed ; and (3) by its presence in the adult stage 

 of the primitive blind family, the Conocoryphidge. 



It is of considerable interest to find a blind species - of the genus 

 Harpes (fl. henignensis, from DcZ 1 Barr.), and its significance will 

 be discussed later. 



With regard to the origin of the eye-spots themselves, it has 

 been explained that it does not seem possible to regard them as 



1 MattheAv, Trans. Roy. Soc. Canada, vol. ii, sect. iv. 

 * Barrande, Syst. Sil. Boh., Siippl., vol. i, p. 4. 



