CYPEIS LARVA OP SACCULINA CARCINI. 627 



takes place exactly in the manner described and figured by 

 Delage (1). In every case the larva was fixed by one of its 

 anteunulte to the base of a hair, most frequently on the legs of 

 the crab, and preference was shown for the sparsely scattered, 

 plumose hairs upon the flat surfaces of the proximal joints of 

 the legs. The larvee appeared to avoid fixing on the dense 

 hairs which fringe the edges of the appendages. This fact 

 is fortunate, since the Cypris when fixed upon an isolated 

 hair on the smooth surface of an appendage is a most con- 

 spicuous and unmistakable object. 



The crabs which I placed with the Cypris to be infected 

 were about 7 — 15 mm. in breadth, and I selected specimens 

 which had recently undergone a moult, since the skin of 

 thes e individuals is clean and easy to manipulate. 



Soon after fixation the Cypris larva casts away bodily all 

 its thoracic appendages with their attached muscles; I was 

 fortunate to obtain this stage, the particular specimen exactly 

 resembling Delage's Plate 23, fig. 21 (2). During the next 

 two days a process goes on inside the Cypris shell which 

 leads to the formation of the Kentrogon larva. According to 

 Delage, the ectoderm of the larva draws away from the 

 Cypris shell and comes to surround a mass of mesodermal 

 cells lying in the anterior region of the body; the ectoderm 

 secretes a layer of chitin externally to the whole, the Cypris 

 shell falls off, and with it the degenerated remains of the 

 larval muscles, pigment, sense-organs, and broken-down food 

 material, and the so-called Kentrogon larva, a little oblong 

 sac encased in chitin, is left attached to the hair of the crab 

 b y^jneans of the antennule of the Cypris. 



Delage's figures representing these changes were so com- 

 pletely reproduced in the larvas observed that I have nothing 

 to add to his description. 



With regard to the contents of the Kentrogon larva a word 

 is necessary. Delage considered that a layer of ectoderm is 

 present surrounding a mass of cells which he calls the ovary. 

 This conception I disputed (2, p. 43) after finding the earliest 

 internal stages of the parasite in which no visible differentia- 



