312 BUIvLETIN OF THE BUREAU OF FISHERIES. 



least it is impossible to apply any theory of fixation which does not involve a fluid 

 cement substance, engulfing both hairs and eggs, capable of setting under sea water 

 and possibly in chemical relation to it into a firm "hydraulic" cement which is non- 

 ductile under ordinary pressures when it is once set. 



I have spoken of the chorion as a tough membrane. That this is true is proved by 

 the vicissitudes through which it passes unharmed. In egg laying the egg is compressed, 

 being rod shaped in some forms when it passes the duct; it is therefore elastic, but it is 

 only slightly ductile and then only when under great pressure. The freshly laid lobster 

 eggs are spherical and as we have seen measure -^t inch (1.5-1.7 mm.) in diameter; 

 the egg embryo when ready to hatch is oblong, and measures about ^ inch (2.1 mm.) 

 on the average of the short and long diameters (fig. 33). This swelling in size, due to 

 embryonic growth, stretches the chorion to great tenuity, until the limit of elasticity 

 and ductihty is reached, and the membrane bursts under the pressure, aided to some 

 extent by the exertions of the larva. 



THE MALE SEXUAL ORGANS. 



The paired testes of the male are either distinct or united by a transverse bridge, 

 and each give off a coiled duct or vas deferens, which opens by a valvular orifice on the 

 inner side of the first segment of the last thoracic leg (fig. 2, pi. xi,iv). The duct con- 

 sists of a proximal division which conducts the sperm from the testes, an enlarged glandu- 

 lar part, and a terminal muscular or ejaculatory segment. A linear milk-white mass 

 marks the course of the sperm through the transparent tube. In the coiled glandular 

 division it is embedded in gelatinous envelopes or spermatophore-sacs (sph.) secreted by 

 the lining epithelium. A sphincter muscle {sp. mu) produces an abrupt swelling at the 

 beginning of the ductus ejaculatorius, the function of which is to eject the sperma- 

 tophores. The latter have the appearance of semitransparent rods of vermicelli about 

 an inch long, and consist only of opaque masses of sperm and the gelatinous medium 

 described. When pressed out artificially, they imbibe water and swell perceptibly. 



SPERM CELLS, THEIR ORIGIN AND STRUCTURE. 



The sperm cells of the lobster (fig. 31) were apparently seen for the first time by 

 Valentin in September, 1837, and he gave a brief account of his discovery in the following 

 year. A more accurate account by Kolliker, who also remarked on the apparent immo- 

 bility of the "rayed cells," appeared in 1843, with figures, and notice of the "seminal 

 sacs" or spermatophores. 



The structure and genesis of the spermatozoa of the lobster have been studied with 

 much detail by Grobben, Gilson, Hermann, Sabatier, and more recently by Brandes (jj), 

 Labbe (173) and Koltzoff (172). Probably few structures in the animal kingdom have 

 been more puzzling than the rayed cells of the decapod Crustacea. The puzzle consisted 

 in harmonizing the following conditions as generally found in these animals. The large 

 eggs of crustaceaus are surrounded by a tough chitinous membrane in which neither pore 

 nor micropyle has been discovered. The sperm cells may be rounded or columnar, but 



