THE AMERICAN LOBSTER. 1 5 ( J 



letter S, passes to the buck of the hist thoracic leg. The sperm may be traced along 

 the course of the tube as a central, milk-white, linear mass of closely packed sper- 

 matozoa. In the glandular segment this is surrounded by a transparent, jelly-like 

 substance which is secreted by the glandular epithelial cells (spermatophoral glands) 

 lining this part of the duct. This is gradually constricted into the terminal (c) muscu- 

 lar segment, or ductus ejaculatorius, which ends in a valvular opening. A sphincter or 

 swelling of the muscular layer is seen at the beginning of the ductus ejaculatorius, 

 serving to force out the sperm. 



The two distal segments (&, c) were called the penis or "verge" by Milne Edwards 

 and Brocchi, because it was supposed that they were evaginated in copulation. It 

 has been already pointed out that the evagination of these parts is mechanically 

 impossible, a sufficient reason for dismissing this supposition. 



The structure of the different sections of the vas deferens is illustrated by plate 

 37. The planes of section are marked in fig. 120, 1 to 5. As Grobben has already 

 shown (S5), the vas deferens is surrounded by a distinct membrane and is composed 

 of a connective tissue wall, inclosing muscles, and a lining epithelium ; the latter gives 

 rise to secretions which mingle with the sperm aud surround it with protective envel- 

 opes. The connective tissue is fenestrated, abounds in blood channels, and the 

 muscular tissue is disposed into an inner stratum of longitudinal fibers and an outer 

 layer of circular bundles. 



At the extreme proximal end of the duct (fig. 124) the epithelium is apparently 

 stratified and the wall is thin. The tube is filled with a solid mass of ripe sperm (sp) 

 and a surrounding coagulable fluid, which is the direct secretion of the epithelial cells. 

 As the glandular segment is approached the epithelium becomes distinctively col- 

 umnar (fig. 125). The glandular segment (figs. 127, 128) is partly subdivided by the 

 infolding of the epithelium (/). The spermatophores (in some cases there are two) are 

 restricted to one chamber and are immediately surrounded by a yellowish secretion 

 (Spr.), which is probably formed in the proximal segment and stains very feebly in 

 carmine. The remainder of the spacious cavity [a and b) is filled with a less dense 

 coagulable siibstance which stains freely in carmine. Bodies resembling yolk-spheres 

 can sometimes be seen. 



Grobbeu says that the secretion of the glandular segment of the vas deferens 

 of the crayfish appears chalky-white in reflected light and consists of small, shining 

 granules. 



In the ductus ejaculatorius (fig. 126) the muscular coats are strongly developed and 

 the epithelium appears to secrete an albuminous, granular substance. The height of 

 the columnar or cylindrical cells varies very much, as Grobben remarks, according as 

 they are squeezed more or less closely together. 



The external opening of the vas deferens is formed by an invagination of the skin, 

 and according to Grobben is paved with thick cuticle. 



SPERMATOPHORES. 



The sperm is ejected from the muscular segment of the vas deferens in the form 

 of spermatophores, which consist of elongated packets of sperm cells, surrounded by 

 gelatinous capsules, the origin of which we have just seen. The spermatophores can 

 be pressed out of the ducts when these are removed from the body. They quickly 

 imbibe water and swell perceptibly when wet with it. The spermatophore is composed 

 of two distinct secretions, as was first pointed out by Grobben. According to the 



