of the inner 
1883. ] | FHeterogenetic Development in Diaptomus. 383 
larged variety or age form of D. sanguincus, but the writer must 
still express his decided belief that these must all be referred to 
the European D. castor. 
It must be admitted that the intensity of coloration does not 
depend upon season but upon the conditions of the water which 
may or may not be influenced by the time of year. In the same 
month I have found the same species of all colors, from colorless 
to deep crimson-red or variegated red, yellow and blue or purple. 
Weissmann seems to have neglected these facts in referring the 
coloration of many species of Cladocera to sexual selection. I 
have found in every case where the Diaptomus was intensely red, 
the species of Cyclops, usually green or bluish, would be more 
or less red; also. In Swan lake, near Decatur, nearly all the 
Cladocera were brilliantly marked, sida and stmocephalus (?) be- 
ing most so; in the neighboring lakes these species were pale 
as usual. 
With respect to the identity of our species. 1st. The armature 
of the last segment of thorax is usually obscured by doubling 
over. Fig. 12, Plate vi of Brady gives the large thorn but omits 
the lower process. 2d. Fig. 7, Plate vı of Brady figures the pro- 
cess on the antenna of male. (Claus gives the best figures.) 3d. 
Fig. 5, Plate 1 of Cyclopide of Minn., Herrick shows that the 
mner branch of the male fifth foot is armed by three spines (as 
figured by Brady) in Minnesota specimens, It must be remarked 
this applies to young forms only, and that the later forms lose 
them and become shorter. Brady has probably transposed his 
_ humbers as regards the female feet of fifth pair. 
The serrature of the spines differs between different age forms. 
Diaptomus pallidus Herrick (Plate vu, Figs. 1-6) is quite rare 
ce veered with the foregoing. The peculiarities mentioned in 
the original notice suffice to distinguish it from any other known 
"9 Me, D. sicilis Forbes, seems to sustain the same relation to 
pallidus that giganteus does to castor. The two-jointed character 
branch of female feet in sici/is confirms this. view. 
oss are several differences however. 
. nar shee-—Extremely slender head separate from thorax by 
fifth fo. » antenne longer than the caudal sete; sete very long ; 
eee of female very short, inner branch with only one ter- 
ao at end; the male fifth feet long; the jaw is like that of 
27 
