ON THE GENUS ANCISTRUMA STRAND (ANCISTRUM MAUPAS)

I. THE STRUCTURE AND DIVISION OF A. MYTILI QUENN. AND A. ISSELI KAHL

¹ COLLEGE OF THE CITY OF NEW YORK

1. Ancistruma mytili Quenn., a holotrichous ciliate commensal in the salt water mussel Mytilus edulis, and Ancistruma isseli Kahl, a holotrichous ciliate commensal in the solitary mussel Modiola modiolus are described.

2. Observations are made from both living and fixed material.

3. The motor system of each consists of long peripheral cilia, a tuft of tactile cilia, and three rows of peristomal cilia all supplied with inter-connected basal bodies. Net-like systems of coördinating fibers occur in the peristomal regions.

4. Each species possesses one micronucleus, which is small and compact.

5. The macronucleus of A. mytili is sausage-shaped while that of A. isseli is spherical. Both are very large.

6. During division the micronuclei divide in the usual manner. They are too small to allow observation of detail.

7. The macronucleus of A. mytili divides evenly and cleanly, while that of A. isseli eliminates a large ball of chromatin at each division.

8. The differences between the two species are discussed.