40^ EMBEYOLOGICAL MOXOGEAPHS. 



31. Radial section of a more advanced germ. The pairs numbered (2) and (3) constitnte tlie sctond series of 



mesenterial septa, the single septum, (4), arising later ; a corresponding single septum (not shown iu tlie 



ligure) arises dianjetrieally opposite (4). , .'. 



Note. — The numbers in parentheses indicate the order iu which tlie brotliers Hertwig claim that 



the septa must have arisen, the septum numbered (4) being in their opinion really a pair of septa. 



Comjjare figures 35 and 36. 



32-34. Actinia equina. From Etienne Jourdan, Recherches zoologiijues ct histologicpies sur les Zoanthaires du 

 Golfo de Marseille. Ann. sci. nat., ser. 6, zooh, Tom. X., Art. no. 1. Oct. ISSO. I'l. XVI. ligs. 117, 118, 120. 



32. Longitudinal section, showing the secondary infolding to form the cesophageal tube (phx). -l^. 



33. Transverse section of a stage with eight partitions {m ut.), of which the iiicinOrana propria forms the axes. V- 



34. Larva with small tentacles, ta. ; cc', ectoderm of the cesophageal tube. 2^1 . ( Longitudinal section. ) 



35. 36. Adamsia dinphaaa. From Oscar Hertwig und Richard Hertwig, Die Actinien anatomisch und his- 



tologiscli mit besonderer Beriicksichtigung des Nervenmuskelsystems untersucht. Jena : Gustav Fischer, 

 1871*. Taf. L figs. 3, 4. 



35. Cross section of a young Adamsia in which the fifth and the sixth pairs of "septa" are still destitute of 



muscle fibres. 



36. Cross section of an Adamsia somewhat older than the preceding. The fifth and sixth pairs of septa, although 



exhibiting muscles, have not yet joined the pharyngeal tube. 



The Roman numerals indicate the ultimate grouping of the septa into pairs in the adult animal. 



The Arabic numerals ai-e used to indicate the supposed order of appearance of the 6 [irimary pairs of septa, 



the 5th and 6th apjieariug, liowever, at the same time. 



The pairs numbered 3, 3, and 4, 4 are called "direction septa" by the Hertwigs. 



37. Thirteen figures illustrating the scissiparity of /(?))/«,«« /ncccreto. From A. Andres, Intorno alia scissipariti 



delle attinie. Mittheilungen a. d. Zoolog. Station zu Neapel, Bd. 111., Heft 1. 9 Dec. 1881. Taf. VIL 



The letters correspond to the successive epochs of observation, as follows : A. 7 Nov. 9 A. M. ; B. 7 Nov. 

 12 M. ; a 7 Nov. 12 : 20 p. M. ; 7). 7 Nov. 12 : 30 P. M. ; E. 7 Nov. 12 : 40 P. M. ; F. 7 Nov. 12 : 50 P. M. ; 

 a. 7 Nov. 1 p. M.; //. 11 Nov. 3 p. M.; /. 12 Nov. 3 p. M.; /. 19 Nov. 10 A. m.; AT. 25 Nov. 3 p. 11. 



The unaccented letters belong to figures giving the general aspect in profile. B, D, and G are natural .size ; 

 /and K, magnilied two diameters, represent only the newly-formed individual. The letters with a single- 

 accent pertain to figures exhibiting the appearance of the base, and those with a double accent to figures 

 o( radial sections. C, E', and G' are magnified between 2 and 3 diameters ; W 5 diani. ; J', and A'', 6 

 diam. ; C", and A'", 15 diam. 



The parent has 96 mesenteries. Of the intermesenterial chambers the 12 primary are designated by the 

 odd numbers from 1 to 23, the 12 secondary by the even numbers from 2 to 24, the 24 tertiary by the 

 accented numbers 1', 2', 3', etc. (not reproduced here), and the 48 quaternary, or spurious, mesenteries 

 are not numbered. Neitlier of the gonidial chambers is involved in the changes. 



At stage B the disk of the foot exhibits a gibbosity which is opaque at the margin. A radial longitudi- 

 nal section shows in this stage, as also in the next (compare C"), that it is due principally to a thickening 

 of the entoderm, which soon occupies all the available space in the chambers. (The ectoderm in C" has been 

 drawn relatively too thick.) The region embraced in the gibbosity is embraced between the numbers 1 

 and 9. 



In the next stage (C and C") tlie gibbosity is distinguished from the rest of the periphery by two angles, 

 which correspond to the two chambers 1' and 8'. 



Ill stage D the angles correspond to the chambers 2 and 8. The laceration of the mesenteries embraced 

 between 3 and 7 now begins. 



In the succeeding stage [E') upon the base the laceration is completed in the median space, and is also 

 extended to the chambers 4 and 8, nearly isolating the gibbosity, which now remains attached by only two 

 delicate cords, — remnants of 3' and 8'. The ragged edges contract toward the principal mass, whether of 

 the parent or the off-shoot, gradually determining the contour. 

 The final separation (C) is effected at points corresponding to 2' and 8'. The process thus far has occu- 

 pied only one hour. 



Four days later (/7') the basal portion of the parent shows the arrangement of restored mesenteries and 

 chambers, and the contour shows that the scar is healed. The ofT-shoot is thickened and rounded ; the mes- 

 enteries at its extremes are fused together into a uniform obscure mass. The chamliers which ]iersist are 3, 

 3', 4, 4', 5, .5', and 6, together with the intervening ones. A sagittal section perpeudicul.ir to the plane of 

 separation shows that the off-shoot has an opening where its continuity with the i>arent was severed. This 

 opening is restricted by the margins of the internal parts, which tend to curve inward at all points and, 



