20.2 IBLA CUM1NGII. 



ordinary Cirripedes the penis is long, articulated, and 

 capable of varied movements, I presume for the purpose 

 of impregnating each separate ovum : the male Ibla has 

 no such organ ; and no doubt the whole body, furnished 

 like the penis with longitudinal and transverse muscles, 

 serves the same purpose ! I may remark, that it seems 

 surprising that so small a male should secrete sufficient 

 semen to impregnate the ova of the female, but the ova 

 are not nearly so numerous in Ibla as in most genera of 

 Cirripedes ; and the smallness of the males in some para- 

 sitic Crustacea has already been alluded to. The male 

 must always be younger than the female, for the latter 

 must first grow large enough for the larva of the male to 

 crawl into her sack. Whether the male lives as long as 

 the female I know not, but he certainly lives for a con- 

 siderable period and increases in size, as shown by the 

 depth to which the end of the peduncle is imbedded. 

 Moreover we shall see, under the next species, that the 

 male is metamorphosed from a larva, not one sixth of its 

 own size. 



In the male Ibla, abortion has been carried to an ex- 

 traordinary and, I should think, almost unparalleled 

 extent. Of the twenty-one segments believed to be nor- 

 mally present in every Crustacean, or of the seventeen 

 known to be present in Cirripedes, the three anterior 

 segments are here well developed, forming the peduncle : 

 the mouth consists as usual of three small segments : 

 the succeeding eight segments are represented by the 

 rudimentary and functionless thorax, supporting only 

 two pair of distorted, rudimentary and functionless cirri : 

 the seven segments of the abdomen have disappeared, 

 with the exception of the excessively minute caudal 

 appendages ; so that, of the twenty-one normal segments, 

 fifteen are more or less aborted. The state of the cirri 

 is curious, and may be compared to that of the anthers 

 in a semi-double flower; for they are not simply rudi- 

 mentary in size and function, but they are monstrous, and 

 generally do not even correspond on opposite sides of the 



