38 



ExMBKYOLOGlCAL MONOGRAPHS. 



PLATE XI. 



Development of Zoantharia (Actinin^e). Figures from Henri de Lacaze-Duthiers, A. 0. 

 KowALEVsKY, Etien'nk Jourda.v, Oscar Hertwig und Richard Hertwig, and Axgelo 

 Andres. 



Arabic numerals are used to indicate the order of appearance of the mesenteries. 

 The Gi'eek letters show the order of the formation of mesenterial chambers and the order of the 

 succession of the tentacles uji to the stage with 12. 



1-25. Adiniamesemlryanthcmum. From Lacaze-Duthiers, Developpemcnt des Coralliaires. Premier memolre. 

 Actiniaires sans polypier. Arch, de Zool. e.xp. et gen., Tom. \. 1872. Plates XI. -XIII. 



1. A portion of an exclusively female mesenterial fold or septum, showing eggs M'ith the gerniinative vesicle, 



and also dark, deeply colored germs no longer possessing a germinative vesicle. 



Note. — In the origimil, more extensive, figure the eggs are shown to be often arranged in series. In 

 the opinion of the author, this appears indicative of their common origin. 



2. A liighly magnified spermatozoon. 



2". Cells from the interior of a testicular capsule, in the condition in which they are found when they are 

 mingled with mature spermatozoa. 



3. One of the reniform testicular capsules from a male mesenterial fold, rujituring and allowing the escape of a 



stream of spermatozoa. ^\-. 

 i. A germ at the time of its escape from the ovary. It appears Inistling with prickles, which it afterwards 



loses. 

 4". Portion of the external layer of the same, more highly magnified. '''}-. 



5. (.'U the bottom of the jilate near the mi<ldle.) A germ in which there is a central deeply-stained mass 



(entoderm), and a peripheral layer (ectoderm) scarcely rose-colored. The depression which will Ije the 

 mouth is indicated by or. The cilia are more strongly developed at the aboral pole. The striiite ajipcar- 

 nnce of the outer layer is caused by the presence of nematocysts which have begun to be developed in it, 

 as well .as by the cilia. About ^p. 



6. An embryo seen in profile, and already presenting one partition (septum) indicated by a vertical line. 



7. Tlie .same as the last ; view of the oral pole. The month is elongated in the manner of a button-hole, the 



long diameter of which is perpendicular to the two septa, marked 1, which have divided the central mass 

 of the embryo into uneipial portions, a and a'. 



8. A slightly more advanced embryo seen from the side. The partitions, and especially the oesophageal pro- 



longation, cause the appearatice at this point of the transversely oval cavity. 



9. A more advanced embryo, in which a second pair of partitions, 2, are visililc. 



10. Embryo showing plainly the division into four compartmc^its. The chamber a' is already removed from the 

 partition, 1, which gave origin to it ; the chambers /3, j3 form with a' a group of three lobes representing 

 the greater of the two original chamliers. 



