THE STURGEONS AND STURGEON INDUSTRIES. 
257 
A third tract of lymphatic tissue is found extending along the free margin of the 
spiral valve. The free margin of this spiral valve or fold is greatly thickened through- 
out its entire course. Cross-sections of the portion of the alimentary canal in which 
this structure is found discloses the fact that the thickening of the edge of the spiral 
fold is due to the presence of a cord of lymphoid tissue, which is indistinctly subdi- 
vided into lobules by strauds of fibrous tissue. That there are true lymph -cells 
present in this part of the fold is readily demonstrated in stained preparations of 
cross-sections of this part of the intestine. Such lymph-cells, are, moreover, appar 
ently migratory and move up and down within the papillae or villi with which the 
intestinal wall is here thickly studded. They probably have an important work to 
perform in taking up the digested nutriment which passes through this part of the 
alimentary tract. The relative proportions of this cord of lymphoid tissue is indicated 
in the partially diagrammatic cross-sectiou of the spiral valve, represented in Fig. 47 
at Ly. 
It is therefore obvious that in the sturgeons we have the lymphatic system quite 
highly developed, more so iu fact than in almost any of the Eiasmobranchs, Teleosts, 
Dipiioans, or Ganoids. No close comparisons with other types can be made with respect 
to the lymphoid structures of the spinal eanal. The closest comparison seems to be 
afforded by the strand of lymphoid tissue overlying the spinal cord of the lampreys. 
With respect to the spleen of the sturgeon, which has been frequently identified 
as pancreas, sections show that it is really lymi^hoid. Large Malpighian boMes are 
discernible in sections, which agree closely with the appearance of those seen in sec- 
tions of the spleen of Selachians, some of which I have been enabled to compare with 
sections of the sturgeon’s spleen through tlie kindness of Mr. W. F. W. McClure, of 
Princeton College. 
8. THE DEVELOPMENT OF THE STURGEON. 
The recently deposited ovum of the common sturgeon measures in diameter. 
That of the sterlet, upon which species the most of our information as to development 
is based, is much smaller, measuring only 2’"“. As already stated, besides the egg 
membrane a glairy viscid substance forms a considerable layer ou the exterior of the 
eggs, which becomes soft and stringy upon contact with water, but hardens later into 
a firm substance which finally cements the ova firmly to whatever they may be brought 
into contact. 
The micropylar apertures appear to be multiple iu the egg of the sturgeon. There 
appears to be one central one in the egg of the common sturgeon, which is surrounded 
by a cycle of others, as represented in Fig. 2, Plate XXXVII. The micropyles from the 
first overlie the dark germinal area, and through these minute openings iu the egg 
membranes the spermatozoa or male elements find their way iu order to impregnate or 
fertilize the egg. The micropyles occupy the central position over the germinal area 
before the egg is mature, and set free from the ovarian follicle iu which it grew and 
ripened. In the species of sturgeons studied by Kowalewsky, Owsjauuikow, and Wag- 
ner seven micropyles were observed. Salensky found from five to thirteen in the eggs 
of the sterlet. 
The segmentation of the egg begins at the dark pole and is unequal, and at first it 
is only partial. Later the segmentation furrows extend through the whole egg, as 
Bull. U. S. F. C., 88 17 
