122 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



fish, some of which, like the menhaden, 1 roam abont in vast schools, straining the 

 water as effectively as the towing net. Daring this period the lobster measures 

 from one- third to two-thirds of an inch in length, and is not only helpless in the hands 

 of its animate enemies, but is subject to a vast amount of indiscriminate destruction 

 from the forces of inanimate nature. (For the further consideration of this subject 

 see pp. 187-189.) 



PARASITES, MESSMATES, AND DISEASES OF THE LOBSTER. 



One of the two parasites known to infest the lobster is a trematode (Stiehoco- 

 tyle nethropis). This was first described by Cunningham, who found it in the intestine 

 of the Norwegian lobster. It has recently been discovered in the American lobster 

 by Dr. Nickerson, to whom I am indebted for the following particulars. The larva 

 of this singular parasite, which is from 3 to 7 millimeters long, is found sometimes to 

 the number of 70 or more embedded in the mucous coat of the intestine about the 

 coecum. It is relatively rare, hardly more than 2 per cent of the lobsters which Dr. 

 Nickerson examined being infested by it. Its position at the hinder end of the 

 alimentary tract seems to argue that it comes in by way of the anus rather than 

 through the mouth. Its final host is probably some species of fish which feeds upon 

 the lobster, but the adult trematode is unknown. It may prove to be of a different 

 species from the larva discovered by Cunningham. 



The only other strict parasite which the lobster is known to possess is the large 

 Gregarine (G.gigantea), which was discovered in the intestine of the European lobster 

 by Van Beneden. (194) 



In 1853 Van Beneden (69) called attention to a small green worm which he found 

 on the eggs of the lobster, and which he supposed was a larva of Serpula. Later, 

 in 1858, he concluded that the animal was not a larva, but a fully developed indi- 

 vidual, which he called Histriobdella homari, placing it among the Hirudineae (69). 

 Foettiuger, a later student of this form (69), proposes to change its name to Histrio- 

 drilus benerfeni, and concludes that is is an Enterocoelian, allied to Polygordius. It 

 is not a parasite in the strict sense. 



Although parasites are rare, the lobster is encumbered with a great variety of 

 messmates, which attach themselves to the external shell. 



Whenever the lobster is confined in inclosures, or compelled for any reason to 

 lead a sluggish life, the common barnacle fixes itself to the arched carapace and begins 

 to secrete its tent-like covering as securely as it might upon a stone; mussels of 

 various kinds insinuate themselves in convenient angles of the shell and joints, small 

 tunicates sometimes becoming attached firmly to the under side of the shell between 

 the legs. Tube-forming annelids, lace-like bryozoa, form incrustations in various 

 parts, and red, brown, and green algse often decorate the antennae and carapace with 

 long streamers which are waved with every movement of the animal. At each molt 

 the lobster of course frees itself completely from these troublesome companions. 



•Regarding the menhaden as an enemy of the larval lobster, I have consulted with my friend, 

 Professor J. I. Peck, who has made a very careful study of the habits of these remarkable fish. He 

 writes as follows: " I have never found lobster larvae in the stomachs of menhaden, and yet it must be 

 remembered that the localities whence my material was nearly all secured were brackish- water inlets. 

 Copepods in all stages of growth are abundant and shrimp of the smallest size were common at New 

 Bedford, but in the material from Buzzards Bay I have never seen lobster larvae." He thinks that 

 the evidence can not be conclusive until menhaden are examined which have fed both day and night 

 in localities which abound in lobsters. 



