1 1 P roceedings of the Royal Society of Victoria. 



exists ill Pluinidaria delicatiila and various other species, and 

 which, present in some forms only of P. setnceoides, may attain 

 in them a thickness nearly equal to the inside diameter of the 

 calycle itself ;* and this view of the structure is completely borne 

 out by an examination of the specimens collected by Mr. Wilson. 

 The liydrothecee are formed on essentially the same plan as those 

 of Lytocarpus phillipinus and many other Statopleans ; that is to 

 say, they form a sac, the proximal part of which lies parallel 

 with the hydrocladium, while the distal portion is sharply 

 recurved, the front wall being thereby doubled upon itself so as 

 to form a deep constriction or an intrathecal ridge in front of the 

 cell. In some species— for instance, Aglaophenia longicornis — 

 the inflected parts of the wall do not quite meet, but leave a deep 

 open angle on the outside of the calycle-front ; in others, such as 

 Lytocarpus phxniceus and AcanthocladiicJii Huxleyi, the hydro- 

 theca is more strongly recurved, so that the two parts of the 

 inflected wall come into close apposition and union, forming a 

 completely internal partition.! In K. mirabilis a somewhat 

 intermediate condition occurs ; the thin wall of the recurved 

 portion is not brought into contact with that of the proximal 

 part, but the external angle formed by the inflection of the sac 

 is entirely fllled up by a solid homogeneous chitine, appearing, as 

 seen in lateral view, as a stout wedge-shaped projection, extending 

 fully half across the diameter of the hydrotheca, from a point 

 immediately below the lip. This ridge, however, is only a 

 tliickening of the adjacent perisarc, as may be readily observed 

 in optical section, where the substance of the ordinary hydrotheca- 

 wall is seen to expand gradually into the thickened ridge, which 

 is bounded by a single contour only, proving that it is not an 

 enclosed cavity, but a homogeneous continuation of the perisai'c. 

 In precisely the same way the perisarc along the front of the 



* Further analogous cases are afforded by the thickening of the stem-internodes in 

 Ohelin geniculala, the almost complete filling-up of the hydrotlieca by perisarc in Hypanlhea 

 and Eucopella, and the thickening of the calycle-wall in Campanula riu caliculata, so as to 

 give the appearance in optical section of two calycles, an inner and an outer, often differing 

 considerably in form from each other. In most instances the extent to which the jierisarc 

 is thickened varies greatly in different examples of the same species. 



t In Haliconmrla superba and its allies the partition is considerably below the aperture, 

 and the mesial sarcotlieca continues in union with the front of the hydrotlieca up to the 

 margin ; the partition or ridge therefore appears to spring fi'om the sarcotlieca, and its 

 homology is not at first sight so obvious as in the species already mentioned. 



