14 EMBEYOLOGICAL MOXOGEArHS. 



PLATE III. 



Development of the Hydroiua, continued. Figures from Louis Agassiz, George J. Allman, 



G. VON Koch, and A. Kowalewsky. 



A. apex. ' Apex. Oiiercular summit of gonau- or. Mciutli. 



(fium. om. Ovum. 



B. hi slo. Blastostyle. P. pr. Club-sliaped body. 



C. can. crc. Circular Canal. Ji- r. tb. Radial tubes. 



cal. Calyx, calycle, hydrotlieca. T. ta. Tentacles of free or unattached form, 



cav. Cavity. gonopliore. 



E. e b. Epililast. >»'■ Tentacles of liydranth. 



e h'. Epiblast of stem. tb. liadial tubes. 



G. (ja. Stomach. ' U. ubr. Umbrella. 



ga. cav. Gastric cavity. 7- Perisarc. 



U. h h. Hypolilast. S. I'crisarc of calycle. 



hb'. Hypoblast of stem. "■ I'"crule-like enlargement of the pedun- 



M. man. Manubrium. cle of the calycle. 



moil. Membrane. 0- Spadix of t!ie sporosac. 



0. CI/. Otocyst. 



Figures 1-5, 6-12% 15, 16, were arranged by A. Agassiz. 

 1-5. OhcUa commisuralis, McCr. From Agassiz, op. cit. Vol. IV., PI. X.XXIV. figs. 13, 13', 16, 17, 18. 



1-5*. Development of the medusa. 



1. Profile view of a medusa bud just forming on the hydroid. tb. C'hymiferous tube. idir. Umbrella. 



2. End view of a bud of the same age. tb. Chymiferous tube. 



3. Two medusa-buds in different stages of growth, e b. Epiblast. h h. Hypoblast. man. Manubrium. 



t b. Cliymiferous tube. ubr. Umbrella. 



4. A medusa-bud, in the calycle, from the blastostyle. c b. Epiblast. hb. Hypoblast, t b. Chymiferous tube. 



ubr. Umbrella. 



5. Free medusa (gonopliore) as it escapes from the calycle (view from below), can. crc. Circular canal. 



man. Manubrium, oci/. Otocyst. or. Mouth, ta. Tentacle. 

 5". ObcUa ijcnkulala, Allm. from Allman, A Monograph of Gymnoblastic or Tubularian Hydroids. Jlaij Soc, 

 1869, p. 35, fig. 10. 



Scvnal zooiJ with ova («)/i.) budding from the radial canal ()•. lb.) nbr. Umbrella. q>. "Spadix of the 

 sporosac." 



6-11. Development of the hydroid head (hydrantli). 



6-11. Clytia POTEitiuM, Ag. From Agassiz, o}>. cil. Vol. IV., PI. XXVIII. figs, i, 6, 7, 3, 9. 



These figures show the successive stages in the growth of the liydranth up to the stage (fig. 11) in w-hich 

 it approximates the form of the adult, cav. Cavity of the calycle surrounding the axis. cal. Calycle 

 (bornycup). c 6. Ejiiblast. c 6'. Epiblast of the pedicle, ^a. Stomach. A 4. Hypoblast, hi'. \\y- 

 pobla^t of tlie jK'dicle. 8. Perisarc. 



I'i'-lS". Development of i«o)Hfffea .fc-iJo.OT. From Allman, op. cil. p. 72. 

 12"-12'. Development of the liydranth. 



12». "Very early condition, in which the bud forms a simide cylindrical ciecal offset from the coenosome." 

 12''. " The distal extremity of tlic bud has become enlarged, so as to present the form of an inverted cone." 



