YOUNG; VKRTirAl. DISTRIBLTION AND PHOTOSKNSITIVK VESICLES 



the population was not migrating during this 

 period. IKMT data lumped into 50-m increments 

 show that most night captures were made between 

 50 and 200 m with peak catches between 150 and 

 200 m. 



Photosensitive Vesicles (Figure 2 A) 



The organs are very similar to those described 

 by R. E. Young (1977) \n Pterygioteuthis micro- 

 lampas. Pyroteuthis addolux has two sets of or- 

 gans. The dorsal organs (the more dorsal set) lie 

 embedded in the posterodorsal wall of the cephalic 

 cartilage and adjacent to the optic lobes of the 

 brain. Each ventral organ lies deeply embedded in 

 the posteroventral surface of the cephalic carti- 

 lage. Except for a thin medial extension on each 

 ventral organ, all organs are thick, compact, and 

 approximately circular to square in outline. The 

 histological structure of the dorsal and ventral 

 organs is similar. The integument adjacent to both 

 the dorsal and ventral organs lacks pigment and 

 thereby forms distinctive "windows" for the pas- 

 sage of light. 



Nerves from both dorsal and ventral organs 

 enter the peduncle complex of the brain and their 

 fibers disperse in the base of the peduncle lobe 

 near its broad junction with the olfactory lobe. 



Pterygioteuthis microlampas Bcrr\ I91.'^ 



X'ertical Distribution (Figure 3) 



The vertical distribution has been described by 

 R. E. Young ( 1977). During the day, 48 specimens 

 captured with the Tucker trawl indicate a depth 

 range of 450 to 575 m; 857r of the specimens were 

 taken between 450 and 500 m. IKMT data lumped 

 into 100-m increments (Table 1) show most day 

 captures between 400 and 600 m. At night 56 

 specimens taken by the Tucker trawl indicate a 

 depth range of 25 to 180 m; nearly 85*^ of the 

 captures were made between 50 and 105 m. IKMT 

 data lumped into 50-m increments indicate a 

 range of to 200 m with a strong peak in the 50- to 

 100-m depth zone. The night distribution was not 

 affected by moonlight (R. E. Young 1977). 



D PV 



POST 



PS MASS 



FIGURE 2.— A. Photosensitive vesicles oiPyroteuthis addolux. This illustration and most subsequent drawings show a side view of the 

 bram. The optic stalk has been cut (as indicated by cross-hatching) and the optic lobe removed. The esophagus can be seen passmg 

 through the bram. Three major subdivisions of the bram are apparent (i.e., the supraesophageal mass, the posterior subesophageal 

 mass, and the middle subesophageal mass.) A large nerve tract which extends anteriorly to the anterior subesophageal mass was cut 

 (indicated by dotted line) and the latter portion of the brain is not shown. B. Photosensitive vesicles of A 6ra/iops;s sp. B. Abbreviations 

 for Figure 2 and subsequent figures of photosensitive vesicles: AV. PV.— Anteroventral photosensitive vesicles; C. PV.— central 

 photosensitive vesicles; DOR.— dorsal; D. PV.— dorsal photosensitive vesicles; ES.— esophagus; GILL— gill; H. RET, M,— head retrac- 

 tor muscles; INT,— intestine; M. S, MASS-middle subesophageal mass of the brain; MV, PV.— midventral photosensitive vesicles; 

 N.-nerve; OP. ST.-optic stalk; PED. L.-pedunclelobe; PIG. S.-pigment screen; POST.-posterior; P. PV. -posterior photosensitive 

 vesicles; P. S. MASS— posterior subesophageal mass of the brain; PV.— Photosensitive vesicles; V. PV.— ventral photosensitive 

 vesicles; S. MASS — supraesophageal mass of the brain; VENT. — ventral. 



587 



