ON THE DEVELOPMENT OF SYNGNATHUS ACUS. 109 



comparative importance. Their sluggish existence 

 in this external womb, where they do not require 

 or receive rapid aeration of the blood, obviates the 

 necessity for that constant action of the jaws that 

 even in the young alevin with unabsorbed sac, in 

 other families of fishes, aids in the development of 

 the muscles of the jaws when there is yet no need 

 for using them for procuring food. We are strongly 

 tempted thus to suggest, that the siphon-tube mouth 

 is the direct consequence of the attempt to keep 

 the young fish too long in leading-strings, more 

 especially as the S. lumbricifovmis (whose mouth, 

 and head in advance of the eye, have no such 

 excessive develorjment as the pre-orbital portion of 

 S. acus) has only external attachment and no pouch. 

 That the pouch may be of comparatively recent 

 development in the family may also be suggested 

 from the great development of eye in the young of 

 & acus, as in other youngsters whose sight is more 

 necessarily acute than in this nursed alevin. The 

 large eye and brain is a marked characteristic in 

 most young creatures, but here they seem to be 

 developed for a totally different set of conditions 

 from those to which the young Syngnathus is 

 exposed. 



Explanation of the Plate. 



Plate I. 



Fig. 1-4. Progressive stages of development of siphon of Syngnct- 

 tJius acus, Lin. 

 5. Head of Adult, life size. 



