38 PROCEEDINGS OF TUE 



Sir Eay Lankester, F.R.S., F.L.S., said lie was not preparer! 

 there and then to discuss points of detail, hut the subject was so 

 interesting that he should wish to offer some remarks. Moreover 

 he gathered from Dr. Gaskell's book, and from more direct in- 

 formation, that he himself was to some extent connected with the 

 genesis of Dr. Gaskell's vie^s, since certain observations and 

 arguments of his own on Limulus and the Scorpion had germinated 

 in Dr. Gaskell's mind and led him to the vpry careful and elaborate 

 studies which he had made and the extraordinary theory which he 

 advanced. AVhilst calling it an " extraordinary " theory, he did 

 not wish it to be supposed that on that account he wished to 

 reject it or not to give it full attention. This was a matter not to 

 be treated as a priori impossible or improbable, but the question 

 simply was, " Are the facts brought forward by Dr. Gaskell such 

 as to make it appear probable that the Vertebrates have developed 

 from Arthropods resembling Limulus by the conversion of the 

 old alimentary canal into the neural tube and the simultaneous 

 formation of a totally new digestive tract ? ' 



The relations of animal forms to one another is the great 

 pi'oblem of morphology. A hundred and twenty years ago morpho- 

 logists still believed in the " scala naturae " and a linear progressive 

 series of animal groups. The great step was taken by Cuvier in 

 opposition to the conception of Lamarck of arranging animal 

 forms in four branches — " embranchemens " he termed them, the 

 Eadiata, Mollusca, Articulata, and Vertebrata. lie thereby 

 anticipated the modern conception of a branching pedigree, which 

 became the generally accepted form of classification when once 

 Darwin had established the tlieory of Descent. 



The earlier attempts at a branching pedigree made by Haeckel 

 differed from the later ones by the same naturalist, and there had 

 been considerable development and improvement in the theoretical 

 pedigree, which aimed at exhibiting the genetic affinities of ail 

 animal forms. The question of the position of the Tunicata had 

 been one of the most interesting. Allman, foi'ty or more years 

 ago, considered the Tunicata as related together with the Polyzoa 

 to the Lamellibranchs and other Mollusca. He regarded the 

 perforated pharynx of the Ascidian as formed by the fusion of 

 the gill-plates of a Lamellibranch along their free edges to form 

 a closed sac, and this was perhaps the largest call upon the 

 imagination which had been made by a modern morphologist until 

 Dr. Gaskell suggested the conversion of the Arthropod's digestive 

 tract into the spinal cord and the formation of a new gut in 

 Vertebrata by the closing in of an open ventral groove. The facts 

 brought forward by Kowalevvsky had determined the position of 

 Ascidians in the Vertebrate stem. There were four " coinci- 

 dences " of structure which by the law of probability led to the 

 conclusion that Ascidians were genetically closely related to 

 Vertebrata. They were the existence in the Ascidian tadpole as 

 well as in Vertebrata (l)of the notochord developed from eudoderm. 



