154 MERISTIC VARIATION. [part i. 



In all cases of supernumerary oviducal openings the normal open- 

 ings were also present. 



These cases are in addition to those received from Mr Benham. 

 So far, therefore, the cases of extra opening amount to over 3 per 

 cent, of females examined. 



Of 714 males examined, only one was abnormal, having no 

 trace of a generative opening on the right side, the vas deferens 

 ending blindly and hanging free in the thoracic cavity. There 

 was no female opening in this specimen, and the abdominal appen- 

 dages had the form characteristic of the male on both sides. The 

 base of the last thoracic leg on the right side bore no enlargement 

 for the genital opening, but was plain and like that of the pen- 

 ultimate leg 1 . 



In cases of females which lacked one of the openings, the basal 

 joint for the leg which should have been dilated and perforated 

 for the opening, was undilated and resembled the basal joint of a 

 penultimate leg. The oviduct upon the imperforate side was 

 more or less aborted and hung loosely in the thoracic cavity. 



In the abnormal females with extra oviducal openings, the 

 oviduct divides generally into two just before it enters the legs, 

 the fork being placed at the level between them. In some few 

 cases no branch of the oviduct could be traced to the extra open- 

 ing. In one specimen the extra opening led into a short tube 

 which ended blindly, not communicating with the oviduct. The 

 specimen (4) with extra openings on the penultimate and last legs 

 had thus in all six oviducal openings. Those in the normal position 

 on the antepenultimate legs were of normal size, those on the next 

 pair were smaller but still of fair size, while those on the last pair 

 of thoracic legs were very small, that on the left side being the 

 smallest and admitting only a fair-sized bristle. In this specimen 

 the single oviduct of each side forked in its peripheral third, 

 giving a duct to each of the first two pairs of openings, but I failed 

 to find any connexion between it and the openings on the last 

 thoracic legs, which were very short blind sacs. 



In all cases of extra oviducal opening the basal joint of the leg 

 is expanded like those of the normal antepenultimate legs, the 

 degree of expansion being proportional to the size of the opening. 

 The normal openings are always the largest, but the extra ones 

 are sometimes almost as large and would easily allow the passage 

 of ova, but occasionally they are too small to let an egg through. 



As regards principles of Homoeotic Variation illustrated by 

 these cases, three points should be especially remarked : 



1 Compare the following : Astacus fluviatilis. Amongst 1500 specimens 3 were 

 found in which the tubercle through which the green gland opens was entirely- 

 absent. The opening itself was not formed and the green gland of the same side 

 was absent. In another specimen the opening was deformed, probably owing to 

 some mutilation. In this and the previous cases the green gland of the other side 

 was considerably enlarged. Strahl, C, Midler's Archiv fiir Anat. u. Phys., 1859, 

 p. 333,^. 



