Robert V. Kesling

Middle Devonian Hollinid Ostracods from the Falls of the Ohio

Although hollinid ostracods from the Middle Devonian Jeffersonville limestone at the Falls of the Ohio have been known for many years, a detailed study reveals a new genus, Flaccivelum, and fifteen new species, belonging to the genera Abditoloculina, Ctenoloculina, Hollina, Hollinella, and Subligaculum. Nine other species, belonging to the genera Abditoloculina, Adelphobolbina, Flaccivelum, Hollina, and Hollinella, have been previously described. Many of the species of Abditoloculina are closely related, but can be distinguished by the number of loculi in the female. Middle Devonian hollinid ostracods from the Falls of the Ohio ROBERT V. KESLING AND REX M. PETERSON Museum of Paleontology University of Michigan Ann Arbor, Michigan

Notes on Zenker's Organs in the Ostracod Candona

MaLe ostracods of Candona and other genera of the family Cyprididae have paired ejaculatory apparatus, commonly called Zenkers organs. These distinctive, voluminous organs lie in the posterodorsal part of the body, one on each side (fig. 8). Each Zenkers organ consists of a central tube, several wreaths of chitinous spines, numerous tiny muscles, and a surrounding cylinder of epithelial tissue. The central tube is composed of epithelium reinforced with numerous hollow chitin rings, closely spaced but allowing the organ to be shortened by contraction of the muscles. Several wreaths of radiating chitin spines are attached to the central tube and laced together by an intricate set of very small muscles. The front and rear wreaths, which form the two ends of the cylindrical organ, are more complex than the others and have funnel-shaped indentations. The central tube is part of the vas deferens. In copulation, the muscles rhythmically contract in sequence to draw the spines together, shorten the central tube, and force the very long spermatozoa through the organ and out of the penis. The male sex system, of which the Zenkers organs are integral parts, is rather complex in cypridid ostracods. Each half of the system is complete and lies on one side of the median plane; it is approximately a mirror image of the half on the opposite side, but is in no way connectecd to it. To show the relationship of Zenkers organ to other male sex organs, one half of the system is here described briefly. The four testes lie in the hypodermis, a thin flap of tissue which spreads out from the side of the body and lines the valve. They are parallel -and, from their syncytia in the posterior part of the hypodermis, curve downward, forward, and upward (fig. 9). At their entrance into the body, the testes unite to form a vas deferens, which has a devious circuit. The vas deferens re-enters the hypodermis at the side of the forehead, curves parallel to the free edge of the valve, and ends blindly in the posterodorsal region. Upon reaching the blind end, spermatozoa reverse their direction and retrace their route to the ventral region where they enter a second branch of the vas deferens, which parallels the first along the anterior margin of the hypodermis (fig. 9). The vas deferens then extends to the rear of the body, loops back and forth a few times, encircles the Zenkers organ, and enlarges to form a seminal vesicle. Zenkers organ lies immediately behind the seminal vesicle (figs. 8-9). It surrounds a short section of the vas deferens. From the rear of the organ a very narrow tube leads into the intricate penis, in which it makes a more or less S-shaped circuit, marked by several enlargements. It terminates at the tip of the inner lobe of the large penis (fig. 9).

Ontogenetic Increase in Archimedean Weight of the Ostracod Chlamydotheca unispinosa (Baird)

To investigate Przibrams Law for living ostracods, speci- mens of Chlamydotheca unispinosa (Baird) from an aquarium culture were weighed in water with a torsion microbalance. For each interval representing an ecdysis between the fifth and eighth instars, the Archi- medean weight increases remarkably close to twice its former value. For the interval representing the ecdysis between the eighth instar and the adult, the increase is slightly more. The greater increase during the final molting probably results from the development of sex organs as maturity is attained.