MEM. M. C. Z., IX. No. 3. — AGALEPHS, POLYPS. 



11 



PLATE II. 



Development of the Hydroida, continued. Figures from Louis Agassiz. 



Mouth. 

 Pigment. 

 Polyp. 



Tentacle of the hydroid. 

 Inside (around the mouth) row of 



hydroid tentacles. 

 Radial tubes. 

 Tentacles. 



Tentacular bulb cavity. 

 Eulargement of the tentacle at the 



union with the border of the bell. 

 Chymil'crous tubes. 

 Tube which lies in the same jiortion 



of bell (sphcroMicre) as that from 



which the tentacle hangs. 

 Umbrella. 

 Velum. 

 Vitellus. 



Vitelline inenibrane. 

 Inverted external wall. 

 Projection of the umbrella near the 



margin. 

 Chitinous perisarc. 



FeruU'-like enlargement of tlie perisarc. 

 Hydroid head. 



The figures on this jilate were arranged by A. Agassiz. 



1-23, from Agassiz, Contrib\itions to the Natural History of the United St.ites, Vol. III. 

 Pis. XVII. figs. 2, 11, 12 ; XVIII. 1, 2, 3, 4, 5, 6, 10, 11, 12, 14, lO^.Vol. IV. 

 PI. XXV. figs. 2, 2% 3, 4, 5, 9, 12, 13, 14, 15. 



1-16. Corync mirabilis, Ag. 



vt. m. Vitelline membrane. 



Outer and inner layer of the liydroid. cb. gm. and 



1. Ovum. nd. Nucleolus, nl. Nucleus, vl. Vitellus. 



2. A medusa bud just beginning to form, c b. and h b. 



hb. gm. Outer and inner layer of the bud. 



3. Bud little older than the last; "stretched longitudinally." c b. and h b. Outer and inner layers of the hydroid. 



eb. gm. and hb. gm. Outer and inner layers of the bud. lb. Beginning of the system of chymiferous 

 tubes. 



4. 5. Bulls more advanced in age, in the latter of which radial tubes have developed, two of which are shown in 



profile, c b. and h b. Outer and inner layers of the hydroid. tb. Chymirerous tube. 

 6. Older bud showing chymiferous tubes from the side and face. cb. Epiblast of liydioid. hb. Hypoblast of 

 the hydroid. hb. gm. Hypoblast of the bud. It will be noticed th.at the latter wouM seem to be the 

 epiblast. I think it is either hypobl.astic or a third layer, — the gelatinous layer (mesoblast ?). tb. Chy- 

 miferous tube in profile, tb'. Chymiferous tube in face. 



