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1. The adult females of the rhizocephalan, Peltogasterella gracilis (Boschma), although they appear similar, are in reality two kinds, large-egg-producing and small-egg-producing females.2. The large eggs develop into large larvae which function as males (larval cypris males). The small eggs develop into small larvae which give rise to adult females.3. In the metaphase plate of the first maturation division of the large male-producing egg 15 bivalent chromosomes are seen, while in the small female-producing egg a univalent chromosome is found beside 15 bivalent chromosomes.

Observations were made of the chromosomes of the burrowing barnacle Trypetesa lampas (Hancock). A method of squash preparation was used, which incorporated staining the material in a solution of 2% orcein in 45% acetic acid. The diploid number of chromosomes of T. lampas was found to be 12 and the haploid number 6, in both males and females. No obvious chromosomal mechanism of sex determination was found. There was, therefore, no cytogenetic confirmation of Kuhnert's view (1934) that the sex of the larva is predetermined genetically. During mitosis in the females and embryos of Trypetesa lateralis Tomlinson and Kochlorine floridana Wells and Tomlinson, the diploid number of chromosomes was found to be about 14. The numbers of chromosomes in the 3 species of Acrothoracica studied were approximately half those observed in all 12 species of Thoracica and all 5 species of Rhizocephala previously investigated.

[Une femelle adulte de Peltogasterella gracilis (Boschma) produit exclusivement soit de grands œufs, soit de petits œufs. Les grands œufs se developpent en grandes larves dont les fonctions sont celles des mâles larvaires. Les petits œufs donnent naissance a de petites larves qui se developpent en femelles adultes. Le cycle biologique est represente sous forme de diagramme dans la figure 1., Une femelle adulte de Peltogasterella gracilis (Boschma) produit exclusivement soit de grands œufs, soit de petits œufs. Les grands œufs se developpent en grandes larves dont les fonctions sont celles des mâles larvaires. Les petits œufs donnent naissance a de petites larves qui se developpent en femelles adultes. Le cycle biologique est represente sous forme de diagramme dans la figure 1.]

On the basis of studies of seasonal changes in the infection levels of Sacculina carcini in Carcinus maenas a life history for Sacculina at Millport, Scotland is proposed. This life history differs from that proposed by Foxon (1940) in that the externa is considered only to live for one year, the interna subsequently regenerating a new externa. This life cycle receives support from observations on regenerating externa.

With great pleasure I dedicate the two new species described below to the two Amsterdam zoologists Prof. L. F. DE BEAUFORT and Prof. J. E. W. IHLE, who with their important researches in various branches of zoology both have so largely contributed to the progress of this science. The two species described here are parasites of Scylla serrata (Forsk.); they are the only specimens until now known to infest this species of Portunid crab.

HAEMOGLOBIN dissolved in the blood plasma has been recorded in all the major divisions of entomostracan Crustacea except one1. This respiratory blood pigment has been found in all species of Phyllopoda examined, in most Cladocera, in a few Ostracoda, in some harpacticid and parasitic Copepoda and in some Rhizocephala, but not hitherto in the Branchiura. This is a small group of so-called fish lice, which includes the well-known Argulus foliaceus (L.). I have been unable to detect haemoglobin in the pale blood of species of this genus, but Dolops ranarum (Stuhlmann) has red blood and I find that it shows strong absorption bands of oxyhaemoglobin. The animals were fouhd parasitizing the siluroid fish Bagrus docmac (Forskal) in Lake Victoria, and I was able to examine them, thanks to the staff of the East African Fisheries Research Laboratory at Jinja, Uganda.

The common hermit crab Pagurus longicarpus Say is parasitized at Woods Hole by two species of EPICARIDEA (a suborder of isopod crustaceans). A bopyrid, Stegophryxus hyptius Thompson, occurs attached to the abdomen and an entoniscid, Paguritherium alatum Reinhard, is found within the haemocoele. Simultaneous parasitism by both the bopyrid and the entoniscid is, however, of rare occurrence. Stegophryxus causes no external modifications of the host, neither does it effect any marked reduction of the gonads. Paguritherium, on the other hand, brings about complete castration of female hosts and more or less complete atrophy of the male gonads. The pleopods of infested males are unmodified, but those of infested female crabs, while normal in number, resemble the male type more than they do the type characteristic of normal adult females. The effects of RHIZOCEPHALA and EPICARIDEA on the secondary sex characters of hermit crabs as reported in the literature fall into four categories: I. Male pleopods modified; female pleopods unaffected. By RHIZOCEPHALA: Pagurus cuanenis (Nilsson-Cantell, 1926) and Pagurus prideauxii' (Potts, 1906; Baffoni, 1947). By EPICARIDEA: Pagurus bernhardus (Giard, 1887; Bonnier, 1900) and Pagurus prideauxii (Baffoni, 1947). II. Male and female pleopods both modified. By RHIZOCEPHALA: Pagurus meticulosus (Potts, 1906) and Pagurus samuelis (Shiino, 1931). III. Male pleopods unaffected; female pleopods modified. By RHIZOCEPHALA: Pagurus bernhardus (Giard, 1887; Guerin-Ganivet, 1911). IV. Male and female pleopods both unaffected. By RHIZOCEPHALA: Anapagurus chiroacanthus (Nilsson-Cantell, 1926) ; Pagurus pubescens (Reinhard, 1942). By EPICARIDEA: Pagurus longicarpus (Thompson, 1901). No case has been reported in which a female pagurid manifested alterations in its secondary sex characters under the influence of an epicaridean parasite and only a few instances, based on scarce material, where the presence of a rhizocephalan parasite affected the external characters of the female alone. It was therefore thought worth while to study the female pagurids infested with Paguritherium and analyze as completely as possible the modifications of the pleopods with respect to the size of the host, the amount of deviation from the normal and the precise nature of the changes to discover whether the alterations were a retention of the juvenile condition, a state of female intersexuality, or some other phenomenon.