CYTOLOGY OF HYDRACT1N1A AND PENNAR1A. 2IQ 



This cavity increases in extent as segmentation continues. After 

 a time the peripheral cells begin to segment in such a manner as 

 to set cells free in this cavity. The direction of the spindle in 

 Fig. 8 shows the method. Fig. 8 was taken from one of the 

 cells shown in Fig. 9 and in each of the remaining blastomeres 

 there is a mitotic figure, so placed as to give rise to a cell that 

 becomes free in the segmentation cavity. The segmentation 

 cavity finally becomes full of cells due to the setting free of cells 

 from the periphery and the subsequent division of these same 

 cells as they lie in this cavity. 



MEMBRANES IN Pennaria. 



First or False Membrane. The absence of a membrane or 

 membrane-like structure in the animal egg is doubted by some 

 notwithstanding that Wilson, '82, Metschnikoff, '86, Hargitt, '04, 

 and others have repeatedly stated that the eggs of hydroids are 

 naked. Brauer, '91, finds in Hydra, after the embryo is formed, 

 two membranes produced by the ectoderm, but the unsegmented 

 egg is naked. Previous studies in Pennaria make no mention of 

 an egg membrane, but the ectosarcal portion of the egg is de- 

 scribed by Hargitt as forming at times a filamentous membrane 

 around the cytoplasmic papillae. Aside from these references no 

 mention is made of membrane in hydroids. 



When the eggs of Pennaria are well fixed in Bouin, and a 

 haematoxylin stain is followed by a plasma stain such as Bordeaux 

 red, a rather broad but uneven structure is 

 readily observed. It first forms while the 

 egg is still growing and is easily made out 

 while the eggs are still in the medusa. 

 The portion of the egg adjacent to the 

 manubrium shows pseudopodia-like pro- 

 cesses (cf. Hargitt) and between these pro- 



FlG. 4. Outline draw- 



cesses this structure is quite wide and j ng to s h ow trje relative 

 irregular in width. After the eggs are de- thickness and variability 

 posited and have assumed the rounded out- in width of the false mem ' 



brane. F. memb, false 



line, this membrane-like structure appears mem brane. 

 as shown in text-fig. 4. It is rarely of uni- 

 form thickness and usually shows one place that is bulging. Also 



