312 ?• Bestitutionslekre. 



rate of certain dynaniic processes is necessary for the production of certain 

 morphological effects." Lillie (Chicago). 



855) Lewis, R. C, A Study of Pedal Laceration in Actinians. 



(Biol. Bull. 20,2. p. 81—108. 2 figs. in text. 4 plates. 1911.) 

 The observations were based upon three species of Aiptasia and one of 

 Cylista. Pedal laceration appears to be a common mode of reproduction in 

 these, and presumably other Actinians. „The beginning of the process of 

 laceration is characterized by a certain part of the base of an actinian be- 

 coming very firmly attached to the substratum while the animal as a whole 

 moves away from the point which is thus relatively immovably attached. As 

 a result the tissues about this point become strongly stretched and attenuated. 

 With the continuation of the contraction, there finally comes a rupture of the 



tissues at some little distance from the free border of the disc." 



„Immediately after the Separation of the fragment there takes place a 

 rolling-in of the free edges, due principally to the elasticity of the mesoglea, 

 so that for some little distance within the cavity is lined with ectoderm." 



„The change in the form of a laceration piece, leading up to the acqui- 

 sition of the typical actinian shape, takes place through the upgrowth of the 

 tissue about the orifice where it was torn off from the parent. The permanent 

 mesenteries arise as new growths in the undifferentiated tissues of the oral 

 end of the laceration piece. The first twelve mesenteries do not appear in 

 the sequence followed by those in egg embryos. As development goes on the 

 old mesenteries -those brought over from the parent when the fragment was 

 torn off-become restricted to a proportionately shorter and shorter part of the 

 base of the young actinian until they are finally entirely resorbed. The 

 mesenteric filaments are formed, just as in egg embryos, from a downgrowth 

 of the ectodermal lining of the stomodeum. Their trilobed condition arises 

 through the differentiation of this tissue. The tissues of the most actively 

 growing part of a laceration piece become very thin; the ectoderm and the 

 entoderm lost all apparent cell boundaries; the mesoglea arises as a direct 

 continuation of that present in the older tissues. The newly formed tissues 

 contain a very small number of gland cells and nematocysts. These two types 

 of cells are developed to the usual number after the tissue relations have 

 become stable. Lillie (Chicago). 



856) Child, C. M., Further Experiments on Adventitious Reproduc- 

 tion on and Polarity in Harenactis. 



(Biol. Bull. 20,1. p. 1—13. 11 figs. 1910.) 



This paper is supplementary to earlier work on the same subject publi- 

 shed in the Journal of Experimental Zoölogy 7, 1902. The phenomena were 

 exhibited in short cylindrical pieces of the body of Harenactis, from which 

 the mesenteries and mesenterial muscles were removed; such pieces contract 

 so as to bring oral and aboral ends together and these unite so as to form 

 rings. The line of union which is at first on the inside of the ring becomes 

 turned on to the outside, and tentacle groups arise from or near the line of 

 union. As many as six or seven groups of tentacles may be formed on a 

 Single ring. The largest number of tentacles observed in a group was six- 

 teen, twenty four being the usual number in the entire animal. 



"The new outgrowths on the rings represent a more or less close approach 

 to new individuals and involve the establishment of new polarities and sym- 

 metries. They are to be regarded as a form of reproduction related to the 

 formation of adventitious structures in plants. The localization of the out- 



