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



29 



PLATE Vin. 



Development of the Acraspeda. Figures from Louis Agassiz. 



ift.i Tube passing railially from stomach 

 to vicinity of sense organ, open- 

 ing at the periphery into the en- 

 largement (lb) and centrally into 

 radial tube (/6"). 



tb.^ Tube passing directly from stomach 



to bundle of tentacles. 



tb.^ Tube from stomach in sense octant, 

 before division. 



tb.* Centripetal tube arising from circu- 



lar canal at the jieriphcral end, 

 ending blindly at the other ex- 

 tremity. 



tb.^ Tube in the lappets of the oto- 



cyst (?). 



th.^ Angle in tube (J.b) which later 

 pushes itself into the lappet. 

 U. ribr. Umbrella. 

 V. vel., vel.^ Velum. 



vt., vt.^ Vitellus. 



vt. in. . Vitelline membrane. 



a. Him of the orifice leading into ova- 



rian cavity. 



/3. Base of attaclinicnt, also abnormal 



unattached bases. 



/S.' Base of a Strobila with large num- 



ber of con.strictions. 



7. Chitinous basal support (perisarc ?) 



fjf.' Gelatinous portion of the umbrella 

 between two chymifei'ous tubes. 



<p. Phacellcn (sexual filaments). 



tf>.< Phacellcn, seen through the ova- 



rian opening. 



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

 1-9. Aurelia flavidula, from Agassiz, o^;. cit.. Vol. III. PI. X. figs. 1, 2 ; PL X". figs. IG, 17, 19, 20, 22, 23, 24. 

 1-21. Development of the planula from the o\iini. 



1, 2. Ovum (life-size) from ovary. The early conditions are passed through in the ovary and folds of the mouth. 



3. Enlarged view showing the yolk cells in the middle of the ovum. 



4. The vitelline cells occupy the whole vitellus (vt). 



5-8. Consecutive stages, with nucleus (iil) and nucleolus (nd). vt., n/.l Vitellus. vl. m. Vitelline membrane. 

 9. Morula, nl. nucleus, vl. Vitellus. 



10-20. Acrasjicdote medusa, Genus ? These figures resemble the stages of segmentation of Cijanea. They illus- 

 trate the formation of a blastosphere (Hg. 20) from an egg where segmentation has just begun. 



