276 LECTUKES ON BIOLOGY 



But even among these lazy animals we find a great number 

 which for a considerable time carry their brood with them. 

 Some of the starfishes protect their growing young under their 

 bent spines. In the Ophiuroidea the eggs pass a large part of 

 their development in the bursa, a thin-walled air-sac ; several 

 species of starfishes form a kind of breast-pocket by bending 

 back their arms, and in many Holothurians the young develop 

 either in the body-cavity or under calcareous spines which 

 have been specially formed for that purpose on the dorsal 

 surface. 



Most highly developed among all vertebrates is the care of the 

 offspring among the social insects, in particular, ants, bees, and 

 termites. It is remarkable that among these animals the nursing 

 is not done by the parents but by a specific asexual worker 

 caste, or more accurately, a caste in which the sex-organs have 

 become degenerate. These facts, however, are so universally 

 known that I need not deal with them in detail. The familiar 

 spider, which is such a notoriously bad wife that after impregna- 

 tion she kills and eats the male without ceremony, exhibits a 

 touching care for her eggs : there are, in fact, only very few 

 classes of animals in which the care of the offspring is regarded 

 as such an important function as among spiders. Many spiders 

 construct for their eggs ingeniously spun bags which they attach 

 to leaves and branches of different plants. These webs are often 

 so constructed that they closely resemble in shape and appear- 

 ance the fruit of the plants to which they have been fixed, a fact 

 which enables them, of course, more easily to escape their natural 

 enemies. Among other species of spiders the females are not 

 satisfied with this passive care, but fasten the egg-sac to their 

 abdomen and continually carry it about with them. 



Crabs exhibit a similar care for their young. Most people 

 have probably seen a female crayfish, at any rate when boiled, 

 firmly grasping with its little abdominal feet a large number of 

 minute round eggs. 



Fishes are regarded by most men as unintelligent and stupid, 

 but when we see the truly touching and devoted care which 

 many species bestow upon their offspring, and if in particular we 

 observe the common stickleback (Gasterosteus aculeatus) during 

 spawning time, we shall not be inclined to agree with this 



