INTRODUCTION. 



XXXIX 



pereion, whilst auotlier is iuserted beneath tlie posterior 

 margin of the fourth or fifth segment. Grasping the 

 female in this way, the male draws it into immediate 

 contact with itself, so that the dorsal surface of the female 

 presses against the ventral surface of the male. In this 

 attitude, more or less firmly compressed, they swim about 

 or rest on any convenient surface for many days. If the 

 two be driven asunder through fear of any danger, the 

 female seeks a place of shelter, while the male swims 

 more actively about. Should the male swim within some 

 little distance of its late companion, it becomes imme- 

 diately aware of the circumstance; and we have seen it, 

 after having passed the spot, abruptly turn back, seek her 

 out, and seize her with avidity from amidst a numerous 

 mass of others. Immediately after securing, he strikes 

 her with two or three strong lashes of his tail. The 

 female, rolling herself closely up, is carried off by her 

 more powerful mate. 



This contact between the two sexes is either occa- 

 sionally repeated, or it may last 

 throughout the entire period of incu- 

 bation. We have frequently taken 

 them so coupled, even when the young 

 have been so far developed as to be 

 enabled to leave the care of the 

 parent. We are induced, from this 

 fact, to believe that a series of broods 

 may take place successively through 

 the year, and that the erotic state of 

 the female may exist during the period 

 of incubation. 

 The penis (Fig. 15) is a soft membranous tube, that 

 terminates in a small orifice. It probably has, under 

 certain conditions, the power of becoming harder, but 



