The Lake and Brook Lampreys of New York 489 



PLATE VII. FIG. 27-41. 



A series of transections near the middle of the body to show the 

 changes in the gonads (ovary and spermary) at various stages of growth ; 

 atrophy of the intestine in the breeding season ; nest building, and the 

 oral tentacles and velar fold of a larva. The scale is indicated after the 

 number of each figure. 



Structures appearing in all the transections.all abbreviations on Fig. 27. 



A. Aorta. 



C. V. Cardinal veins. 



G. Gonad. The reproductive gland (ovary in the female, spermar\' 

 in the male. ) G. On each section. The ovary and testis are single, 

 foliated organs in the lamprey, and are supported by a fold of peritone- 

 um, Mesogonad, frequently called raesorchium in the male, mesoariuni 

 in the female. 



/. Intestine. /. On all sections. 



IM. L. Intermuscular ligaments between the myotomes. 



K. Kidney and ureter. 



M. Y. Myel, or spinal cord. 



M. A. Mesenteric artery. 



M.G. Meso Gonad. The duplicature of peritoneum supporting the 

 ovary {mesoariuin) or spermarj' (inesorchium). 



M. P. Muscle plates cut transversely. M. P. on Fig. 27, and 36. 

 Each myotome is made up of a multitude of muscle-plates or lamellae, 

 each in a delicate connective tissue-sac. Only the empty sacs are 

 shown in the figures. 



M. T. Myotome or myomere. These overlap like tiles, so that in 

 a transection of the body the cut ends of several appear. The over- 

 lapping myotomes are connected by the intermuscular ligaments {IM. 

 L.). 



M. V. Mesenteric vein. The mesenteric vein and artery are in the 

 typhlosole. 



N. Nucleus. On Fig. 29 A. 



NC. Notochord. 



T. Typhlosole, or spiral intestinal valve ; letter on Fig. 27 and 37. 

 The tissue of the typhlosole appears to be largely lymphoid in charac- 

 ter, lu the figures of the larva, the typhlosole is shown clearly to be a 

 linear invagination of the intestine, thus forming a ridge. Commenc- 

 ing somewhat cephalad of the base of the left dorsal fin, the typhlosole 

 or spiral valve extends cephalad as a right-spiral, and caudad as a left- 

 spiral. 



Fig. 27. (X 2>-2). Transection of an adult male lake lamprey taken 

 in December, to show the size and appearance of the spermary about 

 six months before the spawning season. The intestine also shows the 

 size and general structure in the feeding specimens. 



Fig. 27, A. (X53and7oo). A. Sperm mother-cell showing the multi- 

 tude of sperm-cells within it. B, C. Individual sperm-cells magnified 

 703 diameters, to show their structure and appearance. In B, from an 

 osmic acid preparation, two black spherules are shown in the darker 

 part. D, A red blood-corpuscle with its eccentric nucleus, at the same 

 magnification as B, C, to show the relative size of sperm-cells and red 

 blood-corpuscles. 



Fig. 28. (X 20). Figure of the edge of a lamella or lobule of the 

 spermary, from the same specimen as figure 27, to show the appearance 

 of the sperm mother-cells by reflected light. By comparing with figure 



