42 THE OCEANIC HYDROZOA. 



was incomplete, both the hydrophylhum and the reproductive organ of the terminal zooid being 

 imperfectly developed. 



The two genera Ahyla and Calpe were established by Messrs. Quoy and Gaimard" to 

 include certain species of Calycophoridce which they met with in the Straits of Gibraltar, 

 in Bass's Straits, and elsewhere, and which were distinguished from Biphyes by the irregularly 

 cuboidal form and small proportional size of the anterior nectocalyx. 



Eschschoiz, justly perceiving tiiat no difference of generic importance existed between 

 Abyki and Calpe, suppressed the latter name in the 'System der Akalephen,' and united 

 all the species into the one genus Ahyla^ which he characterised thus : " Ductus nutritorius 

 tubulis pluribus obsitus ; pars corporis natatoria cavitate parva natatoria interna, extrorsum 

 se aperiente, instructa." 



The genus thus defined contained the two species A. pentagona and A. triyona (neither of 

 which was observed by Eschschoiz himself) ; and Eschschoiz adds, as a doubtful appendix 

 to the genus, the two Rosacea of Quoy and Gaimnrd, which, however, are nothing but 

 detached nectocalyces of Praya. 



In a previous work (' Isis,' 1825) Eschschoiz had established another genus of DiphydcB, 

 Aylaisma, having the following diagnosis : " Tubulus suctorius unicus ; pars corporis nutritoria 

 cavitate parva natatoria interna instructa." And this genus he retains in the ' System.' 



Leuckart, during his investigations at Nice, met with some individuals of the Aylaisma of 

 Eschschoiz, which he considers distinct from the A. Baeri of the latter writer, and terms 

 A. pentayoium. His description of the nectocalyx agrees down to the smallest particulars with 

 the structure of the corresponding part in the species of AhyJa at present under description ; 

 and he shows that this so-called Aylaisma is essentially nothing but the detached anterior 

 nectocalyx oi Ahyla pentayona, the precise result to which I was led in a different way in 1849. 



Leuckart considers that this '^Aylaisma-hvm" of Ahyla is not a regular stage in the 

 development of the animal ; but that an adult Ahyla has undergone mutilation — that it has 

 lost its coenosarc and inferior nectocalyx — and while in the act of reproducing them, 

 necessarily takes on the Aylaisma form. In one "Aylaisma" he found a second polypite, with 

 its tentacle, budding from the neck of the ordinary one ; and he states that a more or less 

 developed rudiment of the inferior nectocalyx is always present. 



This was certainly not the case in my specimens, and I suspect Leuckart has fallen 

 into error in describing the rudimentary inferior nectocalyx as a "four-sided" pyramid. 

 (Z. U., p. 52.) Gegenbaur appears to have made similar observations to those of Leuckart and 

 myself. He says (' Beitriige,' p. 14): "I have often seen young, entire Ahyla peitlayo/ue with 

 only one polypite ; and young Diphyes in the same condition." So that he regards these 

 "Aglaisma-forms" as young, and not as mutilated adults. 



Leuckart's careful investigations enable me to add some other particulars of interest 

 to my account of the structure of Ahyla pentayona. I did not trace the four canals which are 

 given off from the short nectocalycine duct of the superior nectocalyx. But, according to 



^ 'Annales des Sciences Naturelles,' t. s, 1827. 



'^ Esclischolz retained AbijJa because he considered the form so named to have been more completely 

 observed. But there is another reason for suppressing the name Calpe, in the fact that it had been 

 applied by Treitschke to a genus of Lepidoptera in 1825 (Agassiz, Index, p. 176). 



