FINAL REMARKS 493 



relationship to monkeys in general. By this method very evident 

 blood-relationships have been demonstrated, especially between 

 members of the Mammalia. 



I therefore started upon an investigation into the possibility of 

 proving relationship in this way between Limulus and Aminoccetes, 

 with the kind assistance of Mr. Graham Smith. I must confess I 

 was not sanguine of success, as I thought the distance between 

 Limulus and Ammoccetes was too great. Dr. Lee, of New York, 

 kindly provided me with most excellent serum of Limulus, and 

 the tirst experiments showed that the anti-serum of Limulus gave a 

 most powerful precipitate with its own serum. Graham Smith then 

 tried this anti-serum of Limulus with the serum of Ammoccetes, and 

 to his surprise, and mine, he obtained a distinct cloudiness, indicative 

 of a relationship between the two animals. This, however, is not 

 considered sufficient, the reverse experiment must also succeed. I 

 therefore, with Graham Smith, obtained a considerable amount of 

 blood from the adult lampreys at Brandon, and produced an anti- 

 serum of Petromyzon, which gave some precipitate with its own 

 serum, but not a very powerful one. This anti-serum tried with 

 Limulus gave no result whatever, but at the same time it gave no 

 result with serum from Ammoccetes, so that the experiment not only 

 showed that Petromyzon was not related to Limulus, but also was 

 not related to its own larval form, which is absurd. 



Considerable difficulties were encountered in preparing the 

 Petromyzon anti-serum owing to the extreme toxic character of the 

 lamprey's serum to the rabbit ; in this respect it resembled that of 

 the eel. It is possible that the failure of the lamprey's anti-serum 

 was due to the necessity of heating the serum sufficiently to do 

 away with its toxicity before injecting it into the rabbit. At this 

 point the experiments have been at present left. It will require a 

 long and careful investigation before it is possible to speak decisively 

 one way or the other. At present the experiment is positive to a 

 certain extent, and also negative ; but the latter proves too much, for 

 it proves that the larva is not related to the adult. 



Some day I hope this " biological test " will be of use for 

 determining the relationships of the Tunicata, the Enteropneusta, 

 Amphioxus, etc., as well as of Limulus and Ammoccetes. 



The origin of Vertebrates from a Pakeostracan stock, as put 

 forward in this book, gives no indication of the systematic position 



