600 F. A. POTTS. 



account of the well-marked secondary sexual differences and 

 tlie frequent ecdyses^ allowiug the ruodifying influence of the 

 parasite on the secondary sexual characters to be clearly 

 demonstrated. But that in cases of this phenomenon the 

 parasite and the host may belong to any phylum is shown by 

 such varied instances as the brittle-star Amphiura parasitised 

 by Oi'thonectids and a copepod crustacean, the Hymenopteran 

 insect Andrena infected by the parasitic strepsipteran Stylops, 

 the mollusc Lymntea by Trematodes, and the crab Inachus by 

 the gregarine Aggregata.^ 



In his conclusions Giard recognises a tendency of the 

 secondary sexual characters of either sex to become modified 

 toward the type of the other under the influence of parasitism, 

 while at the same time those originally possessed may tend to 

 be effaced. Thus in the Oxyrhynchid crab Stenorhyuchus 

 phalangium, attacked by Sacculina f raissei, the male 

 almost entirely loses its copuhitory styles and assumes, in 

 greater or less degree, the abdominal ovigerous appendages 

 proper to the female ; in the female these last-mentioned 

 characters become less accentuated, and the abdomen gradu- 

 ally approximates to the appendageless condition of the 

 male, Giard regarding this as a true modification toward the 

 male type. In other cases, as, for instance, Pala3mon infested 

 by Bopyrid Isopods, there is a different type of effect, the 

 parasite merely preventing the full development of the 

 secondary sexual characters of the male, causing them to re- 

 main in the less advanced female condition. In the primary 

 sexual characters Giard observes a reduction in the size of 

 the gonads and suppression of sexual activity, and the altered 

 condition of the gonads he regards as leading in turn to the 

 above-mentioned modification of the secondary sexual char- 

 acters. This sterility of an infected animal is considered to 

 be merely temporary, though satisfactory cases of the re- 

 generation of the gonad and the resumption of the sexual 

 functions, after the death of the parasite, are not quoted. 



1 This case does not occur in Giard's original list, but is the subject of a 

 recent paper by Smith. See BibHography (7). 



