570 



COLLEGE ZOOLOGY 



pouches on her back until they hatch, and 

 the male obstetrical toad transports strings 

 of eggs, wound about his hindlegs, and 

 deposits the newly hatched young in water. 

 The male sea horse is provided with a brood 

 pouch in which the eggs are well protected. 

 Most birds build nests, some of which are 

 hardly more than a few blades of grass, 

 whereas others are really amazing works of 

 art (Fig. 319). The eggs laid in these nests 

 are kept warm or incubated by the female, 

 male, or by both, until they hatch. Several 

 species, for example the cowbird, lay their 

 eggs in other birds' nests, thus forcing the 

 foster parents to incubate them and care 

 for the young. 



Care of young 



Most of the invertebrates and cold- 

 blooded vertebrates do not care for their 

 young, but a few of them do. Young cray- 

 fish remain with the mother for about one 

 month. Worker honey bees attend the larv^al 

 bees with great care; they provide those 

 who are to develop into workers with royal 

 jelly for two days, then a mixture of pollen 

 and honey for 5 to 6 days. Those who are to 

 become queens are fed only royal jelly, a 

 nutritious albuminous material. This latter 

 is a secretion of the phar)'ngeal glands of 

 young worker bees. The male fresh-water 

 dogfish builds and guards the nest and the 

 young until they are about 4 inches long. 

 The male stickleback also builds a nest and 

 guards the eggs and young. 



Birds 



Birds and mammals are particularly solic- 

 itous of their young, although this varies 

 greatly in different species. Birds that are 

 able to run about soon after they hatch are 

 precocial; they neither need nor receive as 

 much care as those that hatch in a very 

 immature condition (altricial birds). Al- 

 tricial birds must be fed in the nest for a 

 long time. The whip-poor-will and killdeer 



are examples of precocial birds, and the 

 prairie horned lark and chimney swift, of 

 altricial birds (Fig. 320). 



Mammals 



All mammals care for their young, pro- 

 viding them with protection and nourish- 

 ment (milk) until they can take care of 

 themselves. The egg-laying duckbill of Aus- 

 tralia (Fig. 352A) holds her young to her 

 abdomen with her tail, where they lick or 

 suck from her hair, milk that is secreted by 

 her mammar)' glands. Opossums, kangaroos, 

 and other marsupials (Fig. 351) bring forth 

 young in a very immature condition and 

 protect and nourish them in a brood pouch 

 on the abdomen. Young opossums are only 

 about V2 inch long when born; they crawl 

 into their mother's pouch, where they feed 

 on milk until they are able to creep out 

 upon her back, scurrying in again in case of 

 danger. Among the higher mammals, the 

 young may become independent soon after 

 birth, as in guinea pigs, or they may be born 

 blind and helpless, like mice and kittens. 

 The degree of parental care, in general, in- 

 creases as one proceeds up the vertebrate 

 scale to the more complex forms; and the 

 number of offspring produced annually de- 

 creases. The period of helplessness is of 

 great importance to the young, since they 

 are taught at that time much that the race 

 has learned through the ages. 



SELECTED COLLATERAL 

 READINGS 



Arey, L.B. Developmental Anatomy. Saunders, 

 Philadelphia, 1954. 



Earth, L.G. Embryology. Dreyden Press, New 

 York, 1953. 



Huettner, A.F. Fundamentals of Cotnparative 

 Embryology of the Vertebrates. Macmillan, 

 New York, 1949. 



Patten, B.M. Foundations of Embryology. Mc- 

 Graw-Hill, New York, 1958. 



