272 NATURAL SCIENCE [October 



Some prejudice attaches to the habit of existence in which these 

 creatures indulge. On the other hand, the Parasite in Lucian 

 maintains that his profession and personality are the true charm 

 and glory of social life. The parasite in zoology may urge in its own 

 favour that it is an eminent preacher and teacher of cleanliness, and 

 an unanswered advocate for the theory of evolution. The family 

 Choniostomatidae is at present divided into six genera. Forty-rive 

 species are known, chiefly through Dr Hansen's researches. The 

 first published, however, was Sphacronclla hiickarti, described by 

 Salensky in 1868. Thus, so far as their history is known, it is open 

 to suppose that the whole batch has been specially created within the 

 limits of the present century. But the reverential motive which 

 prompts hypotheses of that kind is surely undermined when they 

 require us to contemplate one set of crustaceans as specially contrived 

 to live and multiply, and another set of crustaceans as specially 

 contrived to be vampyres on the first set, and to stop them from 

 breeding. The latter strange effect produced by the presence of some 

 crustacean parasites on their crustacean hosts was first expounded by 

 Prof. Giard. Dr Hansen finds reason to believe that, as a rule, with 

 the exceptions to which all rules are liable, the Choniostomatidae 

 prevent their entertainers from rearing a family. With the opinion 

 advanced by Giard and Bonnier in regard to the Epicaridea, that each 

 parasite has its particular host, and is found on no other species, he 

 does not fully agree, and he also adduces evidence to show that such 

 a rule is not applicable to the whole of the present group. Certain 

 members of it have been discussed by the French authors just 

 mentioned, and some of their results are subjected to rather severe 

 criticism. This, amid the intricacies of a new subject, will be highly 

 acceptable to the general reader. Apples, for choice, need a subacid 

 flavour. They must not be so sharp as to set one's teeth on edge. 

 As the eminent authors reciprocally compliment one another in the 

 names of the new species, there is evidently here no very desperate 

 quarrel. By the extraordinary patience with which during several years 

 Dr Hansen has been accumulating his observations he is entitled to be a 

 little intolerant of more rapid methods, which cannot fail to be hazardous 

 in a material so difficult. The remark which he quotes on his title-page, 

 " We want facts, not inferences, observations, not theories, for a long- 

 time to come," is from Natural Science itself, so it must be true, and a 

 paragraph of his own, beginning, " Now-a-days many authors have a 

 remarkable weakness for publishing innumerable immature notes," 

 deserves cosmopolitan circulation. In another passage Dr Hansen 

 says, " I confess that, though I honour everybody who is capable of 

 suggesting a theory which proves to be well founded and fertile in 

 results, I have always felt, and, as time goes on, feel more and more 

 distaste for superficial conjectures." But this is almost like saying, 

 "There are too many anglers ; what we want is fish." People will go 

 on angling to please themselves, without regard to what we want. 

 Allowance must lie made for differences of temperament and taste. 

 Some misguided persons hear of the discovery of new families, genera, 

 and species with a stolid want of enthusiasm. They perhaps for 

 their part think nothing important but the course of the nerves or 

 the action of the hepatopancreas. Mr Henslow dismisses the origin of 



