56 



GUIDE TO THE COEAL GALLERY. 



Fig. 181 



Case 3, detached from the flower -like stocks of Athecate Hjdroids come 

 Upright part. ^^^^^ j.]^g Anthomedus(v. ; they have naked eye-spots (Fig. 4), and 

 the eggs are formed in the walls of the manubrium ; see Rathkea 

 fasckulata* a little Medusa which is given off from a small solitary 

 fixed polyp with four tentacles. The early history of ParuMa 

 conka* and Tiara pileata* both of which are Anthomedusoe, is 

 unknown. 



The Medusffi of the Thecate Hydroids come under the Lqitomedusos, 

 (see Ohelia* Case 3, and Model of RImjmatodes thakissina) ; the eggs 

 are formed in the radial canals, and the sense- 

 organs are either eye-spots or " litho-cysts," 

 the latter being vesicles containing a hard 

 concretion which transmits impressions from 

 the outside to delicate " auditory " cells. In 

 certain Hydromediis(B the sense-organs arise 

 on modified tentacles known as tentaculo-cysts. 

 These forms, which come under Haeckel's 

 Orders Tracliomedusoi and Narcomeduscn, have 

 no known " Hydroid history," and in some 

 cases are known to develop direct from the 

 Qgg ; see Carmarina liastaUi (Fig. 20), and 

 Model in Case 3a. Two fresh-water Medusse 

 are known, both of which are Hydromedime 

 Limnocadmm so/rerbii, from the Victoria Regia 

 Tank in the Royal Botanical Society's Gardens, 

 has a shallow umbrella less than half an inch 

 in diameter and with numerous tentacles ; 

 the fixed phase occurs as a columnar polyp 

 about a quarter of an inch in height, simple 

 or branched once or twice ; medusa buds 

 arise from the summit ; the original habitat 

 was probably the Amazon region. The second 

 species, Limnocnida tamjanykcc, comes from 

 Lake Tanganyika ; the umbrella is about 

 an inch across, the manubrium is very 

 wide and shallow, and the stomach-cavity is nearly filled up by 

 the convex lens-like central area of the under surface of the 

 umbrella. 

 U r^Tt ^'art ^^i^^lly the Medusa? of Millepora and the swimming-bells, &c., of 

 ^^^ • the Siphonophora belong to the Hydromedusan type. 



ScYPHOMEDUSAN Medus.e {^Sci/phomedrntc). These include the 



Portion of Astylus show- 

 ing cyclosystems each 

 with a central gas- 

 tropore and zone of 

 slite-like dactyloi^ores. 

 (After Moseley.) 



