78 Miscellaneous. 



Observations on the Development of x\ctinia. 

 By M. Lacaze-Duthiers. 



The author did not observe the deposition of the ova ; all the 

 embryos were furnished with cilia, and consisted of an inner, gra- 

 nular coloured part, and an external layer. It is in the former alone 

 that the changes take place. The embryo is oval, or spherical, and 

 moves rapidly by turning in any direction. 



The first change is a sort of indentation which soon produces a 

 cavity. The central mass is then divided into two unequal masses, 

 by two constrictions which proceed from the circumference to the 

 central cavity, and at this period the orifice of the cavity becomes 

 elongated, its extremities corresponding with the middle of each of 

 the two parts. The inequality of this first division is followed by a 

 similar irregularity in the following subdivisions until twelve are 

 produced. 



The largest of the two parts first divides into three, when the em- 

 bryo presents four lobes. The smaller portion then divides into 

 three, and six divisions are formed. The two lobes of the larger 

 portion nearest to the small one afterwards divide into two, forming 

 eight lobes ; the extremities of the mouth always corresponding with 

 the median lobes of the two original divisions, which now contain, 

 the one five, the other, three subdivisions. The two lobes of the 

 larger portion nearest to the original constriction now divide into 

 two, and the two new lobes are again halved, until the whole consists 

 of twelve divisions. 



At this period the young Actinia is very contractile, and often 

 changes its form ; it moves in every direction, but always keeps the 

 mouth in front. The lobes then become nearly equal, and the ten- 

 tacles begin to make their appearance. They appear at first as 

 tubercles, to the number of six, each corresponding with the cavity 

 of a lobe. The two first are situated at the two extremities of the 

 mouth at the middle of the two original portions. Before the six 

 first tentacles have acquired any great development, six other tuber- 

 cles make their appearance between them, forming the second 

 circle. 



From this moment the mode of multiplication changes ; a new 

 tentacle is developed between each pair, so that the third circle has 

 twelve, the fourth twenty-four, the fifth forty-eight, the sixth ninet}^- 

 six, &c. The multiplication of the cells always precedes that of the 

 tentacles, which are only to be regarded as their external appendages. 

 Their increase takes place in the following manner : — At the middle 

 of the last-formed cell, a partition or constriction is seen, which at 

 first appears simple, but soon becomes double, and the laminae of 

 which bound three cells — two lateral and one central, the latter cor- 

 responding with the old cell, which is thus separated from those with 

 which it was previously contiguous by two new cells produced at its 

 expense. The consequence of this mode of development is that each 

 cell has two partitions^ but that the last cycle is always formed of 

 compartments without proper lateral walls, for those which bound 



