770 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [18] 
useful to man as food, and which, thanks to the patient studies of M. 
Coste, can now be reared in great numbers. 
CRAY-FISH, LOBSTER, ROCK LOBSTER, AND CRAB. 
There is a single edible species of crustacean called the cray-fish, 
which is found in our fresh-water streams. This animal, which it is 
scarcely necessary to describe since it cannot be confounded with, or 
mistaken for, any other aquatic animal in the waters which it inhabits, 
is provided on the anterior pair of limbs with two strong but unequal- 
sized pincers; the abdomen is generally very much developed, the six 
segments composing it being very convex above, furnished with power- 
ful muscles, and supplied below with false feet, movable at the base, 
which serve as swimmerets. The false feet of the male differ somewhat 
from those of the female, and present moreover two pieces which are 
‘formed beneath the first segment, are movable at the base upon a cartila- 
ginous articulation, and generally lie directed forward upon the sternum. 
There are two rolled laminz forming a sort of tube which repesents the 
male copulating organ, and connects with a triple testicle and seminal 
vessels. The female has two ovaries placed one upon either side of the 
body and opening beneath at the base of the first joint of the third pair 
of walking appendages. At the period of spawning thése ovaries become 
elongated and much distended with eggs. Copulation is effected as with 
many species of flies, belly to belly. When the male attacks the female 
he turns her over upon her back and the two then closely clasp each other 
by means of their claws and walking legs. Itdoes notappear that the male 
organs enter into the oviduets of the female, but the semen is simply shed 
upon the plastron and around the orifices of the oviducts, where it sol- 
idifies, allowing, without doubt, the spermatozoa to escape and penetrate 
into the ovaries.* When a female is found full of eggs and with certain 
whitish flakes adhering to the under side of the carapace, itis pretty cer- 
tain that the eggs have beenimpregnated. Spawning takes place about 
two months after fecundation, and the eggs when laid become attached 
to the false feet upon the abdomen. ‘They are secured to the feet by 
means of a membraneous pedicle formed by a prolongation or hardening 
of the envelope or glutinous mass in which the eggs are laid, and are 
held in this position until the young are hatched, and even after this 
period the young cray-fish, soft and delicate, find protection under the 
abdomen of the female, whom they do not entirely abandon until their 
* According to the careful observations of Mr. P. R. Uhler, president of the Mary- 
land Academy of Science, the fecundation of the eggs of the cray-fish is external, or 
after they have left the oviducts; that is, the seminal fluid of the male is emitted, while 
in the position described above, upon the plastron and swimmerets or false ap- 
pendages of the female; the eggs are then discharged from the body, pass back to the 
swimmerets, where they are retained during the incubatory period, and where they at 
once come in contact with the fecundatory spermatozoa and are impregnated.—(Tr.) 
[See ‘‘ The Cray-fish,” by T. H. Huxley. ] 
