ON MQRISIA LYONSI. Ba 
EXPLANATION OF PLATES 22 ann 28, 
Illustrating Mr. Boulenger’s paper on “Mcerisia lyonsi.” 
EXPLANATION OF LETTERING. 
Cord. Stem of Cordylophora. Ze¢. Ectoderm. Hd. Endoderm. End. 
Div. Endoderm of the stomach diverticulum. Hrd. LZ, Wndoderm lamella. 
#.U. Ep. Ex-umbrella epithelium of the medusa. Hydr. Hydranth. Hyp. 
Hypostome. Za#. BY. Lateral bud. Za¢. B?. Lateral bud at a later stage. 
Med. Meduse in various stages of development. Mes. Mesogloa. Nem. 
Nematocyst. Per. Perisarcal investment. R. Can. Radial canal of the 
medusa. &. Can. End. Endoderm of radial canal. Strod. B. Buds formed by 
strobilisation. S.U. Hp. Sub-umbrella epithelium. Tent. Tentacles of the 
hydranth. Zen¢. Cav. Internal cavity of the tentacle. Tent. ZL. B. Tentacles 
of the lateral bud. Zest. Testis. 
Fic. 1.—The tangled colony of the hydroid growing on Cordylophora 
(Cord.). xX 2. 
Fic. 2.—A young colony to show the hydrorhiza with its perisareal invest- 
ment, the latter extending on to the proximal part of the branches and their 
growing points. The larger of the two hydranths bears an asexual bud. 
x 30. 
Fie. 3.—A young medusa with contracted tentacles; the stomach is pro- 
vided with four per-radial pouches, x 10, 
Fie. 4.—An adult medusa with extended tentacles; the diverticula of the 
stomach extend a considerable distance down the sub-umbrellar surface. x 10. 
Fie. 5.—Outline sketch of a hydranth bearing a lateral bud; the latter has 
become of very irregular shape, and has given rise to a small colony without 
becoming detached. Note the two tentacles on the bud. x 30. 
Fig. 6.—Similar to the previous figure. The lateral bud has grown toa 
considerable size, and has given rise to a large hydranth without forming a 
~ hydrorhiza. The hydranth bears several developing meduse and a small 
lateral bud with two tentacles. x 30. 
Fic. 7.—Outline sketch to illustrate the formation of buds by transverse 
fission. A process of strobilisation at the base of a hydranth has given rise to 
a number of nearly spherical buds. x 380. 
Fie. 8.—Transverse section of a tentacle from a hydranth. Seven large 
endoderm cells are seen surrounding a small but distinct cavity. x about 
200. 
