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Show 8 MR. F. II. A. MARSHALL ON [Jan. 14, of M a n lobsters may point to the percentage being related to the locality1. The positions of the additional openings upon their respective legs are approximately the same as those of the normal ones on the fifth legs. In the case of those specimens with three pairs of openings, the most anterior of which are situated on the third legs in the position of oviducal openings, it is clear, if only from the modification of the anterior abdominal appendages, that the specimens are males. The abnormal apertures are sometimes smaller than the normal ones, though they may be even larger. In the case of the single specimen showing seven spermatic apertures, the six posterior openings are of about equal size, while the opening on the second thoracic leg on the left side is very much smaller but still quite obvious. The state of preservation of the majority of the specimens rendered it impossible to determine the structure of the internal genital organs. In the fresh specimens it could, however, in some cases be made out that the apertures opened internally into blind sacs. In a few there appeared to be duct-like extensions of these sacs internally. In a fair proportion the vasa deferentia gave off branches which extended for a short distance towards the abnormal openings. In at least one instance these anterior forks of the vasa deferentia reached the bases of the legs on which the abnormal apertures were situated. Whether there is ever a free functional passage from the position of the forking to the abnormal aperture it is difficult to say with certainty. That Norway lobsters with additional genital apertures have been common in Scottish waters for a considerable number of years, appears from information supplied m e by Professor Ewart, Dr. Beard, Dr. Masterman, and others. Before I began my investigation on the degree of frequency of such abnormal lobsters, Dr. Masterman expressed the opinion that quite 10 per cent, of the specimens he had observed since he had been in Scotland had additional genital openings; and Dr. Beard, who has had occasion to examine a very large number, speaks to me of regular epidemics of this kind of abnormality in some years in the past, the students in the laboratory experiencing great difficulty in distinguishing the males from the females. The only published record, so far as I know, of additional genital openings in Nephrops is a recent paper by Mr. Cole who states that " abnormalities in oviducal and spermatic apertures are by no means uncommon, and I remember examining three specimens, two of which were abnormal and had four supernumerary spermatic apertures occurring as follows :- Third walking-legs. • Fourth walking-legs. • • • Fifth walking-legs. • . " 1 Mr. Bateson informs m e that he has noticed some variation in the de frequency of abnormality in regard to the oviducal apertures in batches of YT procured at various times for the Zoological Laboratory at Cambridge and* * opinion that this variation is probably related to the localities from \»i.- \}S ^ batches were obtained. wnicn the |