ABYLA. 43 



Leuckart, one descends directly from the end of tlic nectocalycine duct alone: the posterior 

 wall of the ncctosac to its mouth. Another passes upwards to the blind end of the 

 nectosac, over which it runs, and down the middle line of its anterior face. The two 

 other canals form an arch, convex upwards, on the lateral faces of the sac, and descend to its 

 aperture, round which all four canals are united by a circular canal. 



The inferior nectocalyx of the Mediterranean Ahyla pentai/ona occasionally attains an inch 

 in length. It has four longitudinal canals {conf. Kolliker, p. 46). To the upper end of the 

 coenosarc a rudimentary accessory nectocaly.x is almost always attached, and the basal part 

 of the coenosarc, as far as the first rudiments of polypites, is ciliated internally. 



Those groups of organs or zooids which are provided with perfectly formed tentacles (and 

 which occur at about the junction of the upper with the middle third of the coenosarc), exhibit 

 two other appendages ; one, the rudiment of the hydrophyllium, and the other that of the 

 reproductive organ. The latter becomes larger and larger, and finally its calyx assumes the 

 form of a four-sided pyramid, while the generative elements are developed within its manu- 

 brium. 



The rudiment of the hydrophyllium assumes at first the form of a trefoil leaf, with 

 a median and two lateral lobes ; and the phyllocyst acquires an elongated figure, with two 

 lateral processes corresponding with these lobes. The inner surface of the hydrophyllium now, 

 according to Leuckart, approaches the coenosarc, and the two lateral lobes bend towards one 

 another as if they were about to embrace it. From this time the lateral lobes grow rapidly, 

 the emargination which separates them from the middle lobe is gradually efl"aced, and thus, 

 when the organ has attained one fifth of a line in length, it lies like a saddle on the coenosarc. 

 The phyllocyst sends a long and slender canal downwards, parallel with the coenosarc, a 

 short process upwards, and two lateral processes at right angles to them. 



" In the stage just described the hydrophyllium (Deckstiick) has, as I have said, the 

 form of a saddle : its lateral alae are as yet isolated, so that the genital capsule — which now 

 measures about one eighth of a line — projects outwards like a campanulate appendage 

 between them. But these lateral alae soon begin to coalesce, and the hydrophyllium enters 

 into a new stage of development. 



" The first traces of coalescence appear at the upper end of the alae, which had previously 

 approached one another in the middle line in front of the coenosarc, and finally meet. 

 The confluence proceeds rapidly downwards and inwards, so that the previously foliaceous 

 hydrophyllium is very soon changed into a solid body, whose axis is traversed by the 

 coenosarc. In the lower half the coalescence is confined to the outer edges of the 

 hydrophyllium. There remains here an internal dome-shaped cavity, whose bottom is 

 pierced by the continuation of the hydrosoma, and, besides the polypite and tentacle, incloses 

 the stem of the reproductive organ. At the point of insertion of the last, which now 

 measures about a quarter of a line, and already has the form of a quadrangular pyramid with 

 a contractile nectosac, the rudiment of a second reproductive capsule has appeared as 

 a simple vesicular body, ^\h of a line long. 



"At the commencement of the process just described, the outer surface of the hydro- 

 phyllium was tolerably evenly curved ; but gradually four longitudinal ridges appear upon it, 

 which run down at regular intervals, become bounded by plane surfaces, and gradually 



