44 THE OCEANIC HYDROZOA. 



change the body into a cuboid, whose posterior surface is continued downwards into a 

 hood-like (Schirmartig) appendage."* 



Gegenbaur (' Zeitschrift filr Wiss. Zool.,' v, p. 451) has objected that the hydrophylUum 

 in Abyla does not grow round and embrace the coenosarc, as Leuckart describes, but remains 

 entirely on the side on which it was first formed ; and witli this conclusion, notwithstanding 

 the latter observer's reiteration of his own view (Z. N. K., p. 23), my own observations lead 

 me to agree. The hydrophylliura figured in PI. Ill, fig. 2 d, in fact, measured about j^th of 

 an inch in length, and yet, in opposition to Leuckart's statements quoted above, it had already 

 assumed the cuboidal form; and assuredly its lateral lobes had not coalesced round the 

 ccEnosarc. On the other hand, it seems very possible that the hydrophyUium may eventually 

 infold the pedicle of the polypite. 



The hydrophyUium attains, according to Leuckart, the length of half a line, while the 

 coenosarc is still entire. The polypite, tentacles, and gonophores associated with each 

 hydrophyUium have also increased in size, and now the smallest shock, or even a sudden 

 contraction of the ccenosarc, is sufficient to detach the group of organs as an independent 

 Diphyozooid, or "monogastric Diphyes." 



Leuckart states (Z. U., p. 60) that he has repeatedly watched this process of 

 separation under the microscope, which results from the coenosarc breaking through 

 midway between every two groups of organs, and that the young Diphyozooid exhibits the 

 projecting stump of the coenosarc for a long time. Eventually the hydrophyUium enlarges to 

 a length of li line, and has the form of a tall four-sided pyramid, with a square superior face 

 and obliquely truncated inferior extremity, whose posterior wall is prolonged into a triangular 

 blade, pointed below, and having a produced point on each margin. The inferior face 

 presents the opening of a wide cavity, which extends upwards to the middle of the organ. 

 The phyllocyst sends off a superior and an inferior narrow caecum, and two very wide 

 lateral branches, which embrace the dome-like roof of the cavity. The calyx of the 

 reproductive organ attains a length of two lines and more, and is marked by four strong 

 longitudinal crests, ending below in strong points. At the upper end is a conical process, 

 whereby the organ adheres to the coenosarc. Not infrequently, beside a gonophore of 

 two lines long, another two thirds of a line in length, and already exhibiting contractions, 

 may be seen. Leuckart terms the fully formed Diphyozooid of Ahyla pentagona, Eudoxia 

 cuhoides. But this organism differs widely from the Eudoxia of Eschscholz, and I believe it 

 to be identical with one of the species of Aglaismoides (infra), which in that case will form an 

 additional synonym of Ahyla pentagona. 



Gegenbaur's account of the zooids of Ahyla pentagona agrees in all essential respects 

 with that just cited from Leuckart, but he describes the phyllocyst as sometimes having four, 

 instead of two, lateral lobes, and states that the inferior extremity is em arginate and not 

 pointed. 



Vogt's figures and descriptions of the zooids before their detachment are not very 

 clear, but coincide, so far as they go, with those of Leuckart and Gegenbaur. In Kolliker's 

 specimens the hydrophyllia appear to have been not yet developed, but he gives the first, and 

 a remarkably clear, description of the nectocalyces and the mode of their adjustment to one 

 another. 



* Leuckart, Z. U., p. 59. 



