284 University of California Publications. [Zoology 



involves both ectoderm and endoderm, there is the same attenua- 

 tion of cells that is shown in Fig. 27. jNIorgan (:02) thinks 

 "it very probable that the closing- process involves an amoeboid- 

 like extension of the coenosarc across the open end." The 

 closure of wounds in Corymorpha will be considered later and 

 a comparison will be made then with the phenomena in 

 2'ubularia. 



The construction of the fenestrated membrane in Corymorpha 

 appears to involve: (1) a local increase in the size (expressed 

 mainly in length) of endoderm cells in a narrow annular zone 

 (Fig. 13), the cells being closely pressed together and fusing 

 laterally; (2) a fusion of the cells by their inner ends (Fig. 

 29, a and c), accompanied by a cessation of their growth; (3) 

 an expansion of the stem in the same region, with a resulting 

 strain upon the partition (Fig. 29c) ; (4) as a result of the 

 strain, the attenuation of the partition cells (Figs. 29 and 31) ; 

 (5) proliferation of membrane cells; (6) formation of fenestrae 

 These events will be considered in their order. 



(1) The increase in size of the bridging cells is a result of an 

 absorption of water. As the bridging cells lengthen the quan- 

 tity of their protoplasm remains practically constant, while their 

 vacuoles enlarge. Water is evidently being absorbed. The first 

 result of the absorption of Avater is an increase in turgidit}^ with 

 a consequent increase in size of the cells. What form the en- 

 larging cells may take seems to be determined in this case by 

 the pressure of contiguous cells and by mutual adhesion. The 

 only necessary factors in the elongation of the endoderm cells in 

 preparation for the formation of the membrane seem to me to 

 be growth (in.3rease in volume) and intercellular adhesion. 

 Whether the rather obscure amoeboid activity which Morgan 

 has suggested in explanation of the closure of cut ends in Tubu- 

 laria stems occurs or not — which cannot be determined in the 

 absence of observations on live animals — it does not appear to 

 be necessary at all in accounting for the results here. The prep- 

 arations from which this conclusion is drawn are in entire har- 

 mony with it. 



