In the Murex shells a strong varix is formed at the edge of the shell lip at regular intervals. But we have only a little knowledge about the growth of it. This is a report on the growth of the body whorl and new varix in Chicoreus asianus KURODA (Muricidae). As shown in Text-fig. 1, the growth takes place rapidly. There are several periods in the growth of the shell : 1. Body whorl formation : 7-8 days. 2. 1st thickening period : about 10 days. 3. Varix formation and 2nd thickening period : about a month. The general outline of varix is formed in less than 2 weeks, and the rest is used for the thickening of shell with slow elongation of siphon. The animal stops to feed for these periods of growth.

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The chromosome numbers in 16 species belonging to 7 families of nudibranchs are reported here. The chromosomes so far reported by preceding investigators are shown in Table 1, and those by the present authors are listed in Table 2. These numbers are uniformly 13 in haploid without exception, and in spite of the remarkable difference in their external morphology, these nudibranchs have the similar karyotype. The spermatogonial chromosomes are regarded as of metacentric nature. The sexual difference of chromosomes is not observed.

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The results of the microscopical and quantitative observations on the contents in the digestive organs of Corbicula sandai in April, August, October and December are as follows : 1. In April and August the contents filled up more than about one-third of the digestive organs, while none of them can be observed in October but much in December. 2. About 37% (weight ratio of dried materials) of contents of food masses are of organic substances. 3. 62∿70% (area ratio) of contents of digestive organs are humus substances, mud and sand, 2∿3% are spicules of fresh water sponges, and the residue-29∿36% are animals and plants. 4. The numbers of genus, species, varietus and forma of animals and plants observed in food contents of digestive organs are... [table] Besides the above indicated plants and animals, spicules of freshwater sponges, and humus are observed in food masses of digestive organs of Corbicula sandai. 5. Diatomeae and Conjugatae are especially abundant. Among Diatomeae, Stephanodiscus carconensis and its variety, and Melosira take the greater part of detected organisms-in August, in the mussels of sandy mud bottom the above mentioned two genera (Stephanodiscus and Melosira) have about 50% of all detected organisms in the food masses, and in other months more than 80%. In Conjugatae, Staurastrum dorsidentiferum var. ornatum take 50∿60% of detected organisms of the mussels of various bottoms in October, and also take the same % in the mussels of sand and sandy mud bottom in December. 6. Feeding ratio in Winter is large compared with that of other seasons, but digestion ratio is small. 7. Food materials in their digestive organs show no marked seasonal differences.

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