280 THOS. H. MONTGOMERY, 



II. Structure of the Male Genital Organs. 



Balfour (1883) has given a good figure of a dissection of these 

 organs (tab. 20, fig. 43); this dissection was of either P. balfouri 

 or of the closely-allied P. capensis. The testis (wrongly interpreted 

 by Balfour as the prostate) lies proximally ; it is a slender, worm- 

 shaped organ of equal diameter throughout, but with a constriction 

 at its distal end where it joins with the seminal vesicle (the latter 

 erroneously regarded by Balfour as the testis). This vesicle is an 

 ovoid or nearly globular sack, of much greater diameter than the 

 testis; on the distal surface of the vesicle joins the proximal end of 

 the vas deferens. In the preparations sent to me were only the 

 testes, vesicles, and portions of the vasa deferentia; so that for the 

 remainder of the apparatus I must give Balfour's description. The 

 two long vasa deferentia join one another caudad : "The right vas 

 deferens passes under both nerve-cords to join the left and forms the 

 enlarged tube which, passing beneath the nerve-cord of its side, runs 

 to the external orifice. The enlarged terminal portion possesses thick 

 muscular walls, and possibly constitutes a spermatophore maker, as 

 has been shown to be the case in P. novae- sealandiae^ by Moseley. 

 In some specimens a different arrangement obtains, in that the left 

 vas deferens passes under both nerve-cords to join the right." Might 

 not one of these arrangements be found to be typical for P. capensis 

 and the other for P. balfouri, seeing that Balfour classed these two 

 species as one? "In addition to the above structures, which are all 

 described by Moseley, there are a pair of small glandular tubes, 

 which open with the unpaired terminal portion of the vas deferens at 

 the generative orifice." 



The testes sent to me by Dr. Purcell varied in size and came 

 from individuals of diâ"erent ages, but all of them, even the smallest, 

 contained all the stages of spermatogenesis. In a note received from 

 my friend Prof. Wm. M. Wheeler of the University of Texas, he 

 writes me: "Apparently the males of P. eiseiti [a Mexican species] 

 are sexually mature at birth." 



1. The Testis. 



The testis is that organ where the generations of the germ cells 

 are found (Fig. 250, Plate 24). The earlier stages, the spermatogonia 

 (Spg), are placed close to its periphery, the spermatocytes (Sp. C) and 

 their mitoses {M.D) in the central axis (where there is always more 



