COURTSHIP AND NURSERY DUTIES. 103 



about, and the causes which have fostered de- 

 velopment of the parental instinct, are points 

 which may be more conveniently left till we 

 have digested the following instances. 



We will begin with an account of those fishes 

 which have acquired the habit of nest-building. 



The stickle-back of our ponds and streams will 

 afford us an admirable object lesson, illustrating 

 the perfection to which the parental instinct has 

 risen amongst the fishes. The stickle-back is 

 more than usually provident, for before he com- 

 mences his courting he provides the home, in the 

 shape of a very perfect nest, to which he proposes 

 to bring his bride (fig. 10). This nest he builds 

 entirely by his own efforts. The sides are raised 

 and finally a top is added, a small hole being left 

 at one side for an entrance. This is certainly 

 remarkable for a fish ; but, if possible, a still 

 stranger fact about this nest is the fact that the 

 materials of which it is constructed are held 

 together by a curious sticky secretion which 

 comes from the kidneys. In a similar way, the 

 nest materials of swifts and swallows are held 

 together by the secretion of the glands near the 

 mouth. The nest being complete, the new 

 householder casts about him for a mate. Having 

 sighted what he regards as one worthy of his 

 attentions, he conducts her, as it has been de- 

 scribed, with tender caresses to the nest, and 

 persuades her to enter through the doorway. 

 This done, she lays therein two or three eggs, 

 then bores a hole through the opposite side of 

 the nest and departs. This second doorway 

 proves useful, for it enables a continuous current 



