. phot, pi z_ â phot pi. 3. Fig. 20. a, the last four abdominal somites and telson of Systellaspis affinis in lateral view. /;, the telson, uropods, and posterior portion of the last abdominal somite in dorsal view, to show the position of the uropod and pleopod boss-shaped photophores and of certain pigment spots. x3-5. pigment spots; T,, 4, 5, photophores borne on the protopodites of the third, fourth and fifth pleopods; photophore just anterior to the base of the uropod. An essential similarity of structure is readily apparent between these photophor
. phot, pi z_ â phot pi. 3. Fig. 20. a, the last four abdominal somites and telson of Systellaspis affinis in lateral view. /;, the telson, uropods, and posterior portion of the last abdominal somite in dorsal view, to show the position of the uropod and pleopod boss-shaped photophores and of certain pigment spots. x3-5. pigment spots; T,, 4, 5, photophores borne on the protopodites of the third, fourth and fifth pleopods; photophore just anterior to the base of the uropod. An essential similarity of structure is readily apparent between these photophores and those similarly situated in Hoplophorus and Systellaspis debilis (Kemp, igioZ*, p. 643), but at the same time there exist noteworthy differences which will be mentioned in passing. Apart from these differences the photophores require little description. The lens of these organs has the same structure as has been seen in Hoplophorus (p. 329) and differs but little from that of Systellaspis debilis. It shows inner and outer layers, and a middle layer with again a less dense central layer (Fig. 21, , Li., ), whereas in S. debilis the middle layer appears to be uniform. The peripheral depression around the lens, noted in Hoplophorus (p. 330) and in Systellaspis debilis (Kemp, 19106, p. 643), is not very well marked, but this may be due to the condition of preservation of the specimen. The longitudinal photophore muscle (Fig. 21, ; cf. Hoplo- phorus, p. 333) has been distinguished, but no circumferential muscle loop like that of Hoplophorus could be discovered. A study of carefully fixed material would in all probability reveal this muscle loop, as it is also present in the pleopod photophores of Systellaspis debilis.
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Keywords: ., bookcentury1900, booksubjectocean, booksubjectscientificexpediti
