666 THE POPULAR SCIENCE MONTHLY. 



Cambridge school Mr. "William Bateson, of Pembroke College has 

 been twice across the Atlantic, in 1883 and 1884, to the coast of Mary- 

 land, U. S. A., in order to study the growth from the egg of Balano- 

 glossus, the most important and (to the zoologist) entertaining of all 

 worms, since it has gill-slits like a fish and rudiments of a backbone. 

 Mr. Bateson has made and already published (in a special supplement 

 of the " Quarterly Journal of Microscopical Science," 1885) a complete 

 study of the development of this worm. It is perhaps as well briefly 

 to mention here that a " complete study " in these questions means the 

 preparation and preservation in alcohol of hundreds of specimens of 

 different stages of growth (often very minute) of the animal under 

 investigation, and the subsequent cutting into series of consecutive 

 slices, each about ^oir or> an mcn thick, of a sample of each of these 

 stages ; the scrutiny of these sections w i# th the microscope, and the 

 reconstruction or building up of the actual structure of the animal at 

 each stage by a mental combination of the sections. 



The expedition undertaken by Mr. Caldwell (who was aided in his 

 equipment by funds from the Government Grant Committee of the 

 Royal Society) is perhaps the most interesting, because the animals 

 which he has gone to study are of large size and already more or less 

 familial. The Ornithorhynchus and the Echidna are hairy quad- 

 rupeds (mammals) peculiar to Australasia, which differ from all other 

 hairy quadrupeds in having, like birds, but a single aperture to the 

 exterior for the intestine and the urino-genital canals, and in having 

 the skeleton of the shoulder-girdle and some other features of struct- 

 ure similar to those of reptiles. Like those of reptiles, their bodies 

 are comparatively cold, instead of being kept to a definite "blood- 

 heat " (100 Fahr.) as are those of all other mammals. It had often 

 been reported, and some kind of evidence had been given to support 

 the statement, that these strange beasts lay their eggs like birds and 

 reptiles, instead of retaining the egg-like structure within the body 

 and allowing it there to develop to a certain condition of maturity as 

 do all other hairy quadrupeds. One of Mr. Caldwell's objects was 

 definitely to ascertain whether these animals lay eggs or not, and, of 

 more importance than that, to examine minutely the whole history of 

 the growth in the egg, and to compare it on the one hand with the 

 corresponding development of birds and reptiles, on the other with 

 that of ordinary hairy quadrupeds or mammals. 



Mr. Caldwell has found out all about the eggs of these animals 

 and collected them in quantities. The Echidna lays a single egg y 

 which she then carries about with her in a pouch formed by a fold of 

 skin on the ventral surface of the body, similar to the kangaroo's 

 pouch. 



The duck-mole, on the other hand, lays two eggs at a time and 

 does not carry them about, but deposits them in her nest, an under- 

 ground burrow like that of the mole. Naturalists are awaiting with 



