100 RROOnDR OF THK AUSTRALIAN MPSEUM. 



Nemittnctjiit n'liij. — Tlie tliick iieinatooyst I'ing is a veiy eonspicnous 

 stfuctnfe ill tlie foi-ni of jiu uiiiiitei'rnpted cushion of iiematocysts ander the 

 circular canal. The nematocysts are tensely packed in a continuous ring, 

 wliich is distinctly marked off from the base of the tentacles. In vertical 

 sections (he ring appears oval in outline with its outer mai'gin placed just 

 beneath the circular canal and its long axis directed inwards and downwards. 

 The nematocysts are of two kinds. There are large oviform nematocysts 

 which measure 23-25 n in length and 17-19 ^ in breadth. Besides tliese 

 lai'ge forms there are smaller, nai-row^ly oval or nearly' cylindrical nemato- 

 cysts, their length and breadth being 8 f^ and 4 fi respectively. The two 

 tvpes are similar to those which occur in the clustei's of nematocysts on 

 the tentacles. 



The nematocyst ring has no connection with the l)ase of the tentacles 

 in any of the species of ( 'iiiJuitcuKt, except I', hinhjaoiii, in wliich the basal 

 portion of each tentacle is covered on its undei- side with a tliick pad of 

 nematocysts. 



Velinii. — The velum is not clearly discernible in the living or preserved 

 whole specimens, but is I'eadily made out in vertical sections wdien it is seen 

 to be composed of a double layer of ectoderm separated by mesogloea. 

 The ectoderm consists of a layer of much flattened cells. The velum is 

 broad, covering in the whole of the snbumbrellar cavity, and is perforated 

 by a circular aperture through which the manubrium may be protruded. 

 The I'im of the velar apeiture usually fits closely around the manubrium 

 but does not fuse with it : or the velum may become drawn out into a 

 funnel-shaped structnie through whicli the manubrium is protiuded so 

 that the mouth is carried well beyond the aperture of the funnel. Some- 

 times the velum is appressed to the body, at otheis it is curved outwards 

 thereby considerably enlarging the subumbrellar cavity. 



AJiiiieiitiinj tritrl . — The manubrium is a very mobile part of the alimen- 

 tai'y tract, and is capable of being extended through the aperture of the velum 

 and protruded for a considerable distance beyond tlie edge of the umbrella. 

 The mouth is situated at the free extremity of the manubi-ium. There are 

 no oral tentacles. Around tlie edge of the mouth the ectoderm foi'nis a 

 thickened ridge, which hears large, well developed nematocyst.s. The endo- 

 derin of the maniibi'iuni is thrown into eight ridges which I'each their maxi- 

 mum extent about the niidille of the manubrial legion. These lidges are 

 of a muscular nature and are arianged in the shape of astar with eight raj's. 

 The Innien of the nianubiinm thus presents a stellate appearance in 

 transverse sections through this region. The rays of the star are nai-row 

 and acute ; in the endodertu between them occur large nematocysts. 'I'he 

 cells of the wall of the inanubriuni are free from pignient-gianules. In 

 the upper pari of the inanubriuin the musculai' lidges j»ass into the endo- 

 dermal ridges of (he stomach, while the ravsof the star liccome contijunms 

 with the stomach divei ticiihi. 



The mouth leads into a lai'ge sac-like stomach, which a( its widest 

 occu[)ies the gieatei' part of the body. The endoderm of the stonnich is of 

 very great thickness and is raised up into eight longitudinal ridges. The 

 endoderm cojisists of niinieious cells heavily ladiMi with pigment-granules, 



