REPORT ON THE AMPHIPODA. 289 



1856. Bate, C. Spence. 



On the British Ecbiopiithalma. [From the Report of the British Association 

 for the Advancement of Science, for 1855. Meeting held at Glasgow in September]. 

 London. 1856. pp. 18-62. Plates XII.-XXII. 



This Report considers the second division of Crustacea as Edrioplithalma, using Leach's term as 

 synonymous with Tetradccapoda of Blainville, and Ohoridopoda of Dana, though recognis- 

 ing that not all sessile-eyed Crustacea belong to the division, and that not all members of it 

 have fourteen legs. Dana's view is accepted that the Lxmodipoda of Latreille cannot rank 

 as an order parallel to the Ampldpoda, but his order of Anisopnda is not approved, the true 

 view being supposed to be that Lccmodipoda and Ajiisopoda should be separated from Ajiqihi- 

 pods and Isopods proper as subordinate groups. 



In a discussion headed " The Homologies," the following opinion is advanced : — " The epistome 

 appears with little doubt to be the inferior aspect of the mandibular ring, which is seen on 

 the external lateral surface of the head, and which can be identified from the fact of its 

 carrying the mandibles. This relation of the epistome to the mandibular segment is not 

 admitted by Mr. Dana, who rather, from analogy with the higher types, than by diiect 

 evidence of the subject before him, identifies the epistome as belonging to the inferior (or 

 external) antennal segments." Two modes of expression are applied to the Amphipod 

 extremity or telson. In one it is spoken of as the twenty-first ring, only " to be contem- 

 plated in the character of an obsolete segment with its rudimentary appendages ; " in the 

 other, " it is a rudimentary appendage, modified upon the type of the preceding three " 

 (pairs of appendages). I may here remark that Milne-Edwards, Hist. Nat. des Crust., pi. i. 

 p. 23, regards the telson definitely as the twenty-first ring or segment. He considers that 

 the cleft telson in certain species of Amphipods offers a strilcing example of the division of 

 a ring into two symmetrical and lateral halves. He adds in a note that this is seen in 

 Gainmarus othonis, Gammarus locusta, &c. ; but tliat in most Amphipods these rudiments 

 of the seventh abdominal segment are completely wanting. This is a very strange observa- 

 tion for him to make, and quite the reverse of the fact. Huxley, The Crayfish, p. 161, 

 regards the telson as a median outgrowth of the sixth abdominal segment, which has 

 become moveably articulated therewith. 



After a detailed account of the mouth-organs, gnathopods and perseopods, Mr. Spence Bate 

 produces many arguments to show that the epimeron or side-plate in the Amphipoda 

 " belongs to the log and homologically is the first joint (or coxa), and that it is not a 

 lateral or separate portion of the annular segments of the body of the animal, and in fact 

 that no side pieces or epimerals exist." He maintains the following propositions : — 



" 1st. That seven joints are the normal number in the legs of all the Malacostracous Crustacea. 



" 2nd. That the branchia is normally an appendage of the leg and attached to the coxa. 



" 3d. That the moveable power of the leg is always between the coxa and the leg, and never 

 between the coxa and the body. 



"4th. That the coxa (the so called epimeral) in AmpJiipoda overlaps the segment to which it is 

 attached, and except by a small portion only, is not united by the whole of the margin in 

 juxtaposition with the segment. 



" 5th. That tliin-e are no epimerals where there are no legs. 



" 6th. That epimerals are found in no other type, except the Edriophihalma among Crustacea." 



It does not seem inconsistent with these arguments to suppose that the first joint of the leg is iti 

 fact coalesoent with the side plate, and that the side plate is a protective outgrowth from 

 the segment. 



(ZOOL. CHALL. EXP. — PART LXVII. 1887.) XxX 37 



