REPORT ON THE CRUSTACEA MACRURA. 925 



tains a granular plasma and numerous clear vesicles scattered through its substance. 

 As a rule a small nucleus is visible close to the wall of the ovum, which is distinctly 

 coloured by alum carmine. The size of the eggs is much the same throughout the whole 

 ovary ; in Sylon challengers (PI. CL. fig. 1) they are nearly spherical, with a diameter of 

 - 06 mm., in Sylon schneideri (fig. 7) they are oval and slightly larger, the dimensions 

 being - 08 by - 06 mm. Here and there between the ovarian eggs, especially in 

 Sylon challengeri, stripes of connective tissue with rather large oval nuclei are 

 visible. 



The visceral mass is inclosed by an epithelium which is truly chitinogenous, and has a 

 chitinous outer wall at its surface. This chitinous membrane — at all events when the 

 animal carries no eggs in the mantle cavity — is pressed against a similar membrane, which 

 forms the inner surface of the mantle. The latter organ consists of two layers of 

 epithelial cells, separated from one another by connective tissue and muscular fibres ; at 

 the outer surface a rather thick and very resistant chitinous membrane is secreted by the 

 epithelial cells, whereas the inner coating of chitin is thin and in not quite full-grown 

 specimens is fused with the exterior chitinous membrane of the visceral mass. At the 

 places where later on the openings of the mantle are formed, a thick, lenticular, chitinous 

 disc (PI. CL. fig. 2) is observed. The chitinous membrane at the surface of the mantle in 

 the same preparation is distinctly double, but when the process of exuviation takes place 

 the outer layer probably carries away the lentiform disc also, and so opens the genital 

 pores. Between the two chitinous membranes of mantle and visceral mass the mantle 

 cavity is formed by a simple parting of the two membranes. 



In the series of preparations of Sylon challengeri, the gland, whose secretion serves 

 probably for gluing the eggs together, is seen to be distinctly developed ; but I observed 

 only one gland, and not two as is the case in Sacculina. One of the sections of the 

 gland is shown on PI. CL. fig. 1, which fairly well corresponds to the description of it 

 given by Delage in the case of Sacculina. He calls it the cement-gland, a name, which, 

 as Giard pointed out, 1 is inexact, for it has quite the function of an " Eikittdriise," 

 or "glande colleterique." It is a tubular gland, much ramified, and very irregularly 

 convoluted, and a kind of chitinous membrane is seen everywhere within the interior 

 of the different parts. The gland as a whole, with the connective tissue between its 

 convolutions, forms a lentiform mass. In Sylon challengeri the opening of the female 

 genital apparatus does not take place, as is the case with Sacculina, by means of a 

 vestibule (the atrium of Delage) situated in the centre of the mass of the gland ; for I 

 did not find a trace of such an atrium in any one of an uninterrupted series of 

 preparations, all the sections being perpendicular to the surface of the lentiform 

 glandular mass. At one side of the gland, however, the epithelium of the surface of the 

 visceral mass forms a distinct invagination (PI. CL. fig. 1, d), and perhaps the opening of 



1 A Giard, Sur l'orientation de Sacculina carcini, Comptes rendus, March 10, 1886. 



