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Show 1895.] ANATOMY OP NAUTILUS POMPILIUS. 685 Fig. C shows the condition in Nautilus, where again the same two ccelomic chambers are visible. Here also a communication has become formed between the two, but the two pairs of ducts to the exterior still persist-the anterior nephridium here still preserving its excretory portion-a more primitive condition than in Chiton, and probably to be correlated with the fact of its having become shut off from the main lumen of the duct. A few irregular apertures in the wall separating the two coelomic chambers point towards the still later condition to be met with in Sepia (D), where the septum has disappeared-a faint rudiment remaining in the form of a transverse fold rising up from the floor of the common chamberl. X. Summarg of Conclusions. 1. The perivisceral cavity in Nautilus is remarkable for the almost equal participation in its formation of both ccelom and haemoccel. 2. The coelom consists of two distinct chambers-genital and pericardial-separated by a perforated septum. 3. Each of these coelomic chambers opens to the exterior by a pair of nephridia. 4. The genital ducts of the Cephalopoda represent portions of nephridia. 5. The ovary is remarkable for its extremely archaic character-• an ovigerous region of the coelomic epithelium, roofed in by a simple upgrowth of the coelomic wall. 6. The ova arise from syncytial masses of protoplasm. 7. The testis is also archaic in character, and similar to the ovary in its main features. Its cavity, however, has become subdivided into numerous delicate tubes for the provision of increased area of the spermatogenic epithelium. 8. The penis is a paired structure, its left moiety, however, remaining rudimentary. 9. A n elaborate buccal nervous system is present. 10. The " inner inferior lobe" is innervated not by a pair of distinct ganglia, but by a continuous nerve-cord. 11. Bound the base of the postanal papilla is a curious system of skin-glands. 12. A prolongation backwards of the nerve-trunk which supplies the gills probably represents the postanal commissure of Amphi-neura. 13. A laminated organ lying below the mouth has a function in connection with copulation-the spermatophore of the male becoming attached to it. 14. The evidence as to the " pedal" nature of the Cephalopod arms appears to rest on insecure foundations, and it seems desirable 1 The view advocated by Grobben (Morph. Stud. p. 39) that the condition in Sepia is the more primitive, and that it represents a stage in the evolution of the condition met with in the other Mollusca, seems to m e untenable. PROC. ZOOL. Soc-1895, No. XLIV. 44 |
