1867.] Zoology and Animal Physiology. 559 



supports.* M. Rouget then asks, " Is this peculiar to the Vorti- 

 ce/Za-stem, or is it the condition of muscular contraction in all 

 animals ? " The matter is worth consideration certainly, and has 

 been considered by many physiologists, who do not, however, all 

 assume the identity of Yorticella-stems and muscular fibres. M. 

 Eouget intends shortly to prove — 1st, that a recent hypothesis, 

 according to which permanent contraction is essentially constituted 

 by a series of successive shocks or vibrations, is in absolute contra- 

 diction to well-observed facts ; 2nd, that a tendency towards extreme 

 contraction is a property inherent in living muscular fibre, a neces- 

 sary consequence of its structure and elasticity ; 3rd, that during 

 life this tendency to contraction is combated by a cause of exten- 

 sion which predominates during the repose of the muscle, is deve- 

 loped in the exchange of the nutritive materials, increases with the 

 activity of their access, diminishes or becomes extinguished by their 

 exhaustion, and may be momentarily susj^ended by all the excitants 

 of muscular contractility — nervous action, heat, the electric 

 shock, &c. 



Do the Hare and Babbit breed together? — Dr. Pigeaux has 

 been making some inquiries into this matter, and believes that 

 never, or quite accidentally and rarely, does the hare breed with 

 the rabbit. The so-called " Leporides " are true rabbits, and not 

 hybrids at all. The belief in the existence of such a hybrid was 

 prevalent among the ancients, and indeed is so among some 

 moderns, but is merely due to the existence of varieties of the 

 rabbit having somewhat the aspect of hares. By keeping hares 

 and rabbits in confinement, and carefully managing them, hybrids 

 may be obtained, and a case is quoted by Dr. Pigeaux. It does 

 not appear, however, that the mule was fertile, and it was, more- 

 over, an unsatisfactory creature in other ways, having from a 

 culinary point of view neither the advantages of the hare's flavour 

 nor the rabbit's whiteness. 



* A better proof than the one given by M. Rouget is that Vorticella (in com- 

 mon with many similar forms, and with the contractile parts of others) extends 

 slowly and contracts rapidly. We know well that if we wish to extend a spiral 

 spring, it is a slow process compared with its contraction. — The Editoks. 



