152 Transactions. — Zoology. 



The most important result arising from the examination of Paranephrops 

 setosus is that its affinity to Palinurus now seems to be placed beyond doubt. 

 Paranephrops and the Parastacidcc generally resemble the Palinurida- in 

 that they have no appendages upon the first abdominal segment ; in this 

 they differ from the crayfishes of the Northern Hemisphere, and from 

 Homarus and Nephrops. The Palinuridce aud the Parastacidm also agree in 

 having hooked seiaa,* while in the Potamobiida and in the lobsters the 

 setae are not hooked. Moreover the branchial formulas of Palinurus and 

 and Paranephrops are almost identical. Taking the presence or absence of 



, the first abdominal appendages as the basis of his classification, Professor 

 Huxley placed the Palinuridce and the Parastacidcc together as the Astyla, 

 while the Potamobiid®, Homarida, etc., together form the Stylophora. This 

 classification is confirmed by the structure of the male reproductive organs 

 in Paranephrops setosus, for these agree in every essential particular with 



I those of Palinurus vulgaris as described by Brocchi.f In both the testes 

 consist of two long tubes united towards their anterior ends by a commis- 

 sure ; both have long convoluted vasa deferentia ; and in both the extremi- 



, ties are greatly expanded. This would appear to be the oldest and most 

 generalized form of tbe male reproductive organs of crayfishes, New Zea- 

 land having preserved the old form in this as in many other cases. In 

 Astacus fiuviatilis the testes are very different in shape ; they are trilobed, 

 two lobes being directed anteriorly, and one posteriorly : thus the two pos- 

 terior portions, which in Paranephrops and Palinurus are quite distinct, 

 appear in Astacus fluviatilis to have coalesced into a single mass. The vasa 

 deferentia of Astacus are much convoluted, but their extremities are not 

 expanded or at least only slightly so. Professor Huxley gives them without 

 any expansion,! but in Milne-Edwards' figure they are slightly expanded. § 

 The male reproductive organs of Homarus vulgaris appear to be intermediate 

 between those of Paranephrops setosus and of Astacus Jiuviatilis, for in them 

 the two posterior portions are close together and apparently confluent, 

 though not so perfectly coalescent as in Astacus ; the vasa deferentia are 

 curiously enough not convoluted, though their extremities are considerably 

 expanded. || 



In accounting for the origin and present distribution of the crayfishes 

 Professor Huxley says :■ — " Let it be supposed that, at some former period 



* Huxley, " On the Classification and Distribution of the Crayfishes." Proceedings 

 of the Zool. Soc., 1878, pt. iv., p. 776. 



t Annales des Sciences Naturelles, Se. VI., ii. 



I " The Crayfish," p. 130. 



§ Hist. Nat. des Crust., Atlas, pi. 12, fig. 14 ; or the artic e " Crustacea " in Todd's 

 Encyclopaedia of Anatomy and Physiology, p. 783. 



|| Milne-Edwards' Hist. Nat. des Crust., Atlas, pi. 12, fig. 15. 



