306 Transactions. — Zoology. 



On re-reading the paper of Professor Huxley's referred to in the fore- 

 going quotation,- it appears to me that Mr. Chilton has been misled by 

 having taken a useful and suggestive table of morphological characters for a 

 natural classification. A very similar table is given in Huxley's paper on 

 Ceratodus,} in which the Ichthyopsida are divided, according to the mode of 

 attachment of the mandible, into Autostylica, Amphistylica, and Hyostylica, 

 but it is certainly not intended to convey the impression that the Dipnoi 

 are more nearly related to the Amphibia than to the Ganoids from the fact 

 that the two former belong to the Autostylica, while Ganoids are hyostylic. 



It is evident from even a casual examination, and is implied, although 

 not stated explicitly, in the paragraph of Huxley's paper beginning : — " Let 

 it be supposed, "J that the PotamobiidcB and the Parastacidce are more nearly 

 allied to one another than is either of them to any other family of Crustacea. 

 To say that the Parastacida are more nearly allied to the Palinuridce than 

 to the PotamobiidcB, because they are astylic, is not more reasonable than 

 to say that Angais is more nearly allied to the Ophidia than to the Lacertida, 

 because it is apodal. In the same way, to unite the ParastacidcB with Pa- 

 linurus, and to separate them from the PotamobiidcB, on the ground that the 

 two former possess a more primitive type of male reproductive apparatus 

 than the latter, is equivalent to grouping Ganoids with Elasmobranchs 

 rather than with Teleosts, because of the abnormal condition of the urino- 

 genital organs in bony fishes. 



What Professor Huxley shows clearly enough is that, while the Homarina 

 are more closely allied to the PotamobiidcB than to the ParastacidcB, the 

 reverse is the case with the Palinuridce. He does not discuss the question 

 of the origin of the latter family, nor say whether he considers its affinities 

 to be, on the whole, Astacine or Homarine.|| It is perhaps an open ques- 

 tion whether true genetic affinities are more clearly indicated by the loss of 

 the first abdominal appendage, and by the structure of the male organs and 

 the seta?, or by the structure of the gills ; but, at any rate, it must not be 

 forgotten that Palinurus agrees with the Homarina in having the podo- 

 branchs completely divided into gill proper and epipodite and thus differs 

 wjdely, in an important structural peculiarity, from the ParastacidcB. 



However, this may be, it is certain that the interval separating Pali- 

 nurus from the ParastacidcB is far wider not only than that which separates 

 the latter from the PotamobiidcB, but than that existing between the Astacina 

 and the Homarina. To hold otherwise is equivalent to denying the value 

 of both anatomy and embryology as guides to genetic affinity. 



* On the Classification and the Distribution of the Crayfishes, Proc. Zool. Soc, 

 1878, p. 752. 



t Proc. Zool. Soc, 1876, p. 24. J Quoted by Chilton, loc. cit., p. 152. 



|| Boas, in the paper referred to above, seems to derive Palinwellus from a Homarine 

 ancestor. 



