April. 1929 



E VOLUT lO N 



Page Seven 



man developed turtlier, but was still very much an to the exalted state we occupy as "Homo sapiens," the 



animal, while the Piltdown man stood at the very dawn Wise Men. 



of the human day. The staa;e is set for the appearance , . , „, ^ ^, . 



. , , . . , , . This IS the secoiia of four articles by Mr. Qeramer on The Alices- 



of true man, well started on his long, upward journey j^^s of Mrdem .Man, the ne.xt being on The Neanderthal Race. 



Mammals That Lay Eggs 



By MAYNARD SHIPLEY 



"PGG-LAYING is usually thought of only !n connec- 

 tion with birds and reptiles. But at the antipodes 

 we meet with queer creatures which possess some char- 

 acteristics of both reptiles and mammals. When speci- 

 mens of these parado.xical animals were first taken tu 

 England, they were forthwith pronounced a fake, on 

 a par with the composite "mermaids" exhibited in those 

 days. 



Exploring in southern Australia, one might conic 

 across a strange creature known locally as the "duck- 

 bill mole" — a specimen of one of the two distinct 

 families of these curious egg-laying mammals — an 

 animal about a foot and a half long, with a broad, 

 shovel-like snout, strongly resembling a duck's bill. 

 The feet are webbed, but differ from the duck's in hav- 

 ing five toes, armed with sharp claws. But the body is 

 well covered with soft dark-brown fur. Frequently 

 the creature may be seen in a sitting posture, supported 

 partly by its large, flat tail. 



The duck-bill is a timid beast, and must be approach- 

 ed very cautiously. Watching its movements, one may 

 see it fill its cheek-pockets with food — chiefly water- 

 snails and bivalves — and then dive into a pond. But 

 it does not come to the surface again, even to take air. 

 though one wait patiently an hour or more for its 

 reappearance. Yet no lung-breathing fresh-water crea- 

 ture can "hold its breadth" for so long. \\'here can tin- 

 queer mammal be? 



At last the secret is out! Mrs. Duck-bill ( Oriiithcr- 

 Iiynclius) has gone to her burrow to lay an egg. Fancy 

 a mammal with soft brown fur going home to lay an 

 egg ! But surely she does not lay her eggs under water ! 

 She does not. But the entrance to her "one-room 

 apartment" is below the water-line, safe from all in- 

 truders. Entering her water-hidden burrow, Mrs. 

 Duck-bill passes through a tunnel wh'ch slopes gently 

 upward for a distance of 25 to 50 feet, where there is 

 a rather large chamber with top ventilation, lined with 

 reeds and rushes. Here in a comfortable nest of soft 

 grasses she lays her two or three eggs, less than an 

 inch long, with flexible, parchment-like shells — of rej)- 

 tilian, rather than bird-like, character. 



The eggs are incubated, as in the case of birds, by 

 the body-heat of the mother — such as it is. For cur- 

 iously and suggestively enough from the standpoint 

 of evolution, the body temperature of the Monotrcmata 

 (to include all the species of this order of mammals) 

 is intermediate between the cold-blooded reptiles and 

 the "regular" warm-blooded mammals ; and. as in the 

 case of reptiles, the body temperature changes to the 

 extent of some 25 degrees Celsius with the rise and fall 

 of the atmospheric temperature. This is in agreement 



with the theory of many zoologists that the Monotrc- 

 mata of today are the somewhat modified descendants 

 of the transition type of animals leading from mammal- 

 like reptiles to reptile-like mammals, thence to a gen- 

 eralized type of the monotremes, on to the pouched 

 animals (Marsupials), and through the latter to the 

 true (Placental) mammals. 



After this glance backwards, to a period some two 

 hundred odd millions of years ago, when egg-laying 

 mammals first came into being, let us return to the bur- 

 row of Mrs. Duck-bill of today. 



Having hatched her family of two or three lusty 



Mrs. Duck-bill Serves Dinner 



duck-bills, from her reptile-like eggs, what next? Will 

 these youngsters follow the example of all other orders 

 of egg-laying animals and begin to "pick up" a living 

 for themselves, like a new-born chick or an infant 

 reptile ? 



The little ones are born with a perfectly good set 

 of teeth, whereas mother duck-bill's dental equipment 

 has disappeared, giving place to broad, horny plates, 

 which line the inside of the "bill." And here is where 

 evolution comes in again — for the original Monotre- 

 niata, whose fossil remains are found in the Triassic 

 rocks, are provided with teeth, even in the adult stage, 

 similar to the teeth of an infant duck-bill today. This 

 is in accord with Haeckel's "biogenetic law." 



Anyhow, though hatched from an egg like a reptile, 

 the queer little duck-bills are mammals, after all : and 

 the infant mammal feeds on mother's milk. And these 

 strangest and most paradoxical of all mammals form 

 no exception to the rule. For though mother duck-bill 

 has no true mammary glands — representing as she does 

 a stage in evolution prior to the appearance of true 

 mammals — she is nevertheless provided w'th modified 

 oil glands which in primitive fashion perform the same 

 useful function. These glands, buried deep in the ab- 

 dominal hair, secrete real milk, through a s'eve-like 

 aperture. Eventually, the "milk-teeth" of the growing 

 youngsters are worn off, and are replaced by plates, 

 "just like Mamma's." 



There is another family of these strange egg-laying 

 mammals, the Echidnas, both in Australia and New 

 Guinea, covered with quill-spines instead of fur. But 

 that is another story. 



