344 Raymond Pearl 



not "a fluid body tending to a spherical shape." On the contrary 

 it has a definite ellipsoidal shape. Is this however in detail 

 the same as the final shape the egg will have after the shell is 

 formed .? 



The bulk of the evidence at present available would appear to 

 point to the conclusion that while the general shape of the egg may 

 be determined before it reaches the uterus the particular form of 

 each individual egg is produced in the uterus. Granting this to be 

 the case the further question arises as to the mechanism of this 

 morphogenetic activity of the uterus. There are clearly two pos- 

 sibilities: {a) the uterus may take an active part, shaping the 

 plastic egg, by means of contraction of its muscular wall, or (b) 

 the uterus may play a passive part, acting simply as a mold with 

 more or less elastic walls into which the fluid egg is, as it were, 

 poured. At first thought it might be supposed that the fact that 

 the muscular layer is markedly thicker^ in the uterine wall than 

 in any higher portion of the oviduct could be taken as evidence that 

 muscular activity plays the chief part in the shaping of the egg. 

 This idea loses any force it might otherwise have, however, when 

 it is remembered that the process of expelling the egg demands 

 an extensive muscular development of the uterus wall. Szielasko 

 ('05) has attempted to decide between these alternatives experi- 

 mentally by injecting fluid under pressure into the uterus from 

 the oviduct end of the organ after previous ligation of the cloacal 

 end. He found that the injected uterus had the form of the egg, 

 and concluded from this that the action of the uterus in shaping 

 the egg is mainly passive and depends simply on the elasticity of 

 its walls. He admits, however, that muscular activity may play 

 some part and in particular (p. 290) points out that muscle action 

 must bring about the closure of the two openings of the uterus 

 while the egg is in that organ. Thompson's theory as to the deter- 

 mination of the form of the egg, without any special discussion 

 of the point, assumes that the muscular activity of the oviduct 

 produces the observed results on the eggs. 



From data which have accumulated in this laboratory as well 



'Cf. Cushny ('02) 



