186 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



intensified, as Darwin believed, through the agency of natural selection. It is evident 

 that no such instinct could thus arise in pelagic animals, "where the cessation of the 

 natural movements through hypnotic or other influences would lead to vertical down- 

 ward motion by the action of gravity, unless such movements were of decided benefit. 

 It may be significant that the phenomenon is seen for the first time in the lobster 

 when it is about ready to sink to the bottom and assume the adult habits. I have not 

 examined a sufficiently large number of the adolescent lobsters, from 1£ to 3 inches 

 long, to say how commonly they exhibit this peculiarity. I believe, however, that it is 

 in this case a sporadic phenomenon, which has not at present become a habit. It is 

 not easy to see, moreover, how. in the environment of these animals, where so many 

 of their enemies are scavengers or omnivorous, it could be of much service, to its 

 possessor when finally established on the bottom. 



THE FOOD OF THE LARVA. 



The food of the larval lobster must necessarily consist for the most part of minute 

 pelagic organisms, such as copepods and crustacean larva?. When watched in con- 

 finement they may now and then be seen giving chase to copepods, sometimes larger 

 than themselves, and often without success. 



The young lobster, however, shows little discrimination in its food. It seems to 

 snap up almost any moving object, living or dead, which it is able to seize and swallow. 

 Thus I have found in the stomachs of the older larvae vegetable fibers, the scale of a 

 moth or butterfly, and fine granules of sand. 



On June 17, 1893, I examined the stomachs of a number of larvae (raised in 

 aquaria) 13 to 14 mm. long, probably in the fourth and fifth stages, and found them to 

 contain the following substances: (1) diatoms in abundance, chiefly Navieula and the 

 long tangled ribbons of Tabelaria; (2) remains of Crustacea, probably parts of young 

 lobsters; (3) bacteria in large numbers; (1) cotton and linen fibers and parts of alga?; 

 (5) amorphous matter, with sand grains. The sediment of the jar contained the same 

 species of diatoms in abundance, and amorphous debris similar to that found in the 

 stomach and intestine. 



The stomach of a larva captured in Vineyard Sound August 12 (length 15 mm.) 

 contained the following organisms: (1) parts of crnstacea; (2) diatoms; (3) shreds of 

 algae. In another young lobster taken at the same time (length 17 mm.) there were 

 (1) parts of Crustacea, (2) large numbers of diatoms, (3) filaments of green algae and 

 thin sheets or shreds of vegetable tissue, (4) the scale of a lepidopterous insect, (5) 

 bacteria, (6) amorphous matter in large masses. 



Messrs. Weldon and Fowler (201) came to the following conclusions after experi- 

 menting with different kinds of food which were thought might be acceptable to the 

 larvae : 



It was definitely concluded from these experiments that whatever food is used must he floating in 

 the condition of small particles at a short distance below the surface, i. e., in the same position as the 

 natural pelagic food of the larvaj of the sea, whether this consist of G'opepoda, other Decapod larvte, 

 trochospheres, fish ova, or other members of the pelagic fauna. As to the other two forms of food tried, 

 the Noctilucaj were apparently eaten, the shrimp larvae (Mysis stage) certainly were attacked, and 

 from the fact that the young lobsters attack and devour each other it is prohable that Decapod larvae 

 form at any rate part of the usual food. The contents of a tow net taken near the Eddystone on 

 August 6, which held a young lobster, consisted chiefly of Megalops and Mysis stages of Decapoda. 



