Development 0/ Gastrosteus spinachia. 491 



parietes being sufficient to effect this ; but it is produced so 

 abundantly that it also often appears to ooze out involun- 

 tarily. Male fishes may often be seen with a glistening, 

 pendulous, conoid mass hanging from the urinary aper- 

 ture, and increasing in size until it becomes detached. 

 Such flask-shaped masses of mucus occur frequently in 

 tanks where these fishes are confined and no opportunity is 

 afforded for nest-building. When, however, an appropriate 

 mass of sea-weeds has been selected by the male, the fish 

 has merely to approach closely, so that the protruding 

 mucus may adhere to a projecting frond, and by passing and 

 repassing round the mass the weaving operation is accom- 

 plished *. Occasionally a rapid ejaculatory movement is 

 observed, and it is interesting to note that the threads are not 

 carelessly superposed, except when necessary for increasing 

 the density of the nest, but are crossed at an angle by the 

 varying movements of the fish, so that rhomboidal spaces 

 are enclosed and a regular reticulum is thus produced 

 (PL XIY. fig._5). 



Often the tightly-drawn thread snaps asunder, though its 

 tenacity is extreme ; the fibres then curl up and form a ter- 

 minal pellet, many of which occur on the surface of the nest. 

 As before remarked, the mucus is not merely a semi-solid 

 plasm, but assumes a funicular character while in the ureters. 

 If one of the cords binding a nest together be examined it 

 will be found to consist of several strands, the cord itself 

 measuring from '0046 inch to "0051 inch in diameter, and the 

 constituent threads from '0008 inch to "00092 inch. These 

 smaller threads again consist of fine homogeneous filaments, 

 which adhere in parallel order. The parallel arrangement of 

 the ultimate fibrils is very striking and quite characteristic 

 (PL XIV. fig. 4)._ 



On the completion of the nest the female deposits the ova 

 in the various chambers (PL XIV". fig. 5, hh). The ovum 

 is disproportionately large, viz. "085 inch in diameter, rarely 

 spheroidal, the form being generally an ellipsoid. The cap- 

 sule does not harden for several hours, its soft tenacious 

 nature, assisted by the ovarian fluid, causing the ova to 

 adhere strongly together. Indeed, after being separated, 

 these ova, when brought into contact again within a few 

 hours, immediately cling firmly to each other. As just 



* The interesting behaviour of the male fish at this time has been 

 described by many observers. His solicitude for the safety of the ova, 

 and especially for the young when hatched, is very remarkable: vide 

 Ransom, this journal, vol. xvi. 1865, p. 449 5 also G. J. Romanes, 

 ' Animal Intelligence,' pp. 243-245, 



