If you read the 2 links I posted it explains that the eggs get laid internally into the abdomen. Internal laying and egg yolk peritonitis are very similar. Here is an excerpt from Merck Veterinary Manual:
Internal Laying
In these hens, partially or fully formed eggs are found in the abdominal cavity. Such eggs reach the cavity by reverse peristalsis of the oviduct. If they have no shell, they are often misshapen because of partial or complete absorption of the contents. Frequently, only empty shell membranes are present. No control or treatment is known. This condition is related to erratic ovulation and defective egg syndrome (see
Defective or Abnormal Eggs in Poultry).
Egg Yolk Peritonitis
Egg peritonitis is characterized by fibrin or albumen-like material with a cooked appearance among the abdominal viscera. It is a common cause of sporadic death in layers or breeder hens, but in some flocks may become the major cause of death before or after reaching peak production and give the appearance of a contagious disease. It is diagnosed at necropsy. Peritonitis follows reverse movement of albumen and
Escherichia coli bacteria from the oviduct into the abdomen. If the incidence is high, culture should be done to differentiate between
Pasteurella (fowl cholera) or
Salmonella infection. Antibiotic treatment of peritonitis caused by
E coli infections is usually ineffective. Management of body weight and uniformity, reproductive development (ovary follicle growth and maturation), and drinking water sanitation are the best preventive strategies.
When hens have too many large ovarian follicles, a problem described as erratic oviposition and defective egg syndrome (EODES) is seen in broiler breeders. This condition is accompanied by a high incidence of double-yolked eggs, prolapses of the oviduct, internal ovulation, and/or internal laying that often results in egg peritonitis and mortality. EODES is prevented by avoiding light stimulation of underweight pullets too early and by following guidelines for body weight and uniformity, and lighting recommendations for each breeder strain. Overweight hens may also have a higher incidence of erratic ovulations and mortality associated with egg peritonitis.