page134

Contents Page

page136

 

                                                    THE INTERLUDE OF CANCER                                           135

 

critical period in a fish or mammal or man is that at which the embryonic organs as a whole first begin to function. The fish begins to feed itself, digesting the yolk by intestinal digestion. The mammal or human embryo begins to do the like (in the absence of food-yolk) by means of the commencing functional activities of the allantoic placenta. At this epoch in the fish the pan­creas gland manifests its activities by the presence of abundant zymogen granules in the cytoplasm of its cells. That these result in the secretion of pancreatic ferments is shown by the digestion of yolk within the gut. Owing to this digestion, the fish, like the mammal, gets ever bigger and bigger. None of the yolk enters its stomach, for this has then as little functional activity as the stomach of a mammal has during foetal life. An internal yolk-sac is formed for the reception of the yolk from the external one, and the yolk-duct opens into the duodenum. This fact alone indicates to the embryologist that the pancreas gland is functioning. In an average marsupial at the critical period this gland certainly begins its functional activities, for the animal is then born, begins its mammary nutrition, and digests the milk. If a certain thing happen at the critical period of a fish, or a marsupial, I know from experience that something corre­sponding to it will take place at the like period in a higher mammal or a man. A fish forms its anus at this period, so does a marsupial, while in the act of being born, and so does a man, although he does not need it for some seven months more. As the pancreas gland begins its functions in a fish or an average marsupial, so it must do in the development of a man. Otherwise there would be no essential unity in the mode of the development. Undoubtedly, under the action of the pancreatic fer­ments, the asexual structures of a fish development begin

page134

Contents Page

page136