Interproglottidal glands, [90]

Intertentacular organ, [469], [473], [508]

Introvert, in Polychaeta, [249], [250];

in Gephyrea, [412], [424]

Investing membrane, in ectoparasitic Trematodes, [57];

in Cestodes, [85]

Ioda, form of head, [278]

Isacis, [163]

Jammes, on skin of Nematoda, [126]

Jaws, of Nereis, [248], [250], [270];