442 The American Naturalist. [May,. 
lateral vessel, and posteriorly with both the right and left vessels 
through an anal commissure. The walls of the vessels are formed of 
(1) an inner endothelial, (2) a circular muscular layer, and (3) an outer 
layer of mesenchymal cells arranged like an epithelium. Between the 
endothelial and the muscular layers are large cells of a hemispherical 
form and peculiar structure, which, at the moment of diastole, stand out 
from the wall of the vessel, and at the time of systole plunge into it.. 
They appear to guide the flow of the blood. 
A connection between the nephridia and the vascular system, such 
as Berger has described for marine nemertines, especiallly for Drepa- 
nophorus, does not occur. 
The Existence of Epitokic Forms in the Annelid Family 
Cirratulidz.’—Two members of this family, namely, Dodecacerca 
concharum Orst. (= Heterocirrus ater Qfg.) and Heterocirrus flavoviridis 
St. Jas. have been found in an epitokic stage, which differs from that of 
certain of the Licoride and Syllidæ: (1) in the possession of very long 
swimming processes in the dorsal branch of the parapodia, (2) in hav- 
ing two highly developed eyes on the cephalic lobe, (3) in the short- 
ness of the feeler of the first segment, (4) in the slightly spatula-form 
of the end of the body, (5) in the irregular coloring, (6) in a different 
musculature, and (7) in the possession of mature sexual products. The 
individuals are of different sexes. In August atokic and epitokic forms 
as well as connecting forms are found side by side. 
A Study of the Form of the Crop of the Libellulide and 
their Larve.’—Recently a number of anatomical observations made 
by the author cited, on the form of the crop, the distribution of the 
“teeth,” etc., in the same, have been made use of for systematic and 
phylogenetic purposes. A series of the larvee and imagines of the 
genera, Calopteryx, Agrion, Pyrrhosoma, Erythromma, Enallagma, 
Ishnura, Platyenemis, Lestes, Gomphus, Æschna, Anax, Corduligaster, 
Diplaz, Libellula, Epophthalmia, Cordulia, and Orthetrum, were 
studied, and as a result the conclusion arrived at that the crop of Colop- 
teryginæ represents the primitive form. This shows sixteen areas irregu- 
larly covered with teeth. A perfection of this form appears in the 
Agrioninæ, in which there is a greater supply and a more regular ar- 
rangement of the teeth. In the case of the genus Lestes there are but 
eight longitudinal folds, a number that in the gomphininæ and æschnin® 
5 Mesnil, F., and Caulbry, M. Compt. Rend. Ac. Sc. Paris, 1896. 
F, Ris. Untersuchung über die Gestalt des Kaumagens bei den Libellen und 
ihren Larven. Zool. Jahrb. Abth. Syst., IX (1896), 596-624. 
