STRUCTURE AND DEVELOrMliNT OF COELUl'LANA. 33 



with two to five (rarely up to seven) testes along each subtentacular 

 canal, while I could find only one or two testes along each subpharyngeal 

 canal and that in rather rare cases in C. bocki (PI. 2, figs. I, 2, 4; te), 

 more commonl}-, there occurs none altogether along this canal in that 

 species; the two remaining species were always devoid of them along 

 the same canal. In living specimens, the testes can be easily found 

 even with the naked e\'e as small whitish spots situated serially along 

 both sides of the tentacular sheath (PI. i, fig. i; te). It happens but 

 rarely, however, that all of the testes in the same canal develop simul- 

 taneously; more commonly we find that, while some testes contain fully 

 developed spermatozoa in quantities, others in the same canal show the 

 sexual cells still in the cellular state. The development of the testes 

 arising in one and the same canal advances as a rule in centrifugal 

 direction, the more peripherally situated testes being always in a less 

 advanced stage of development than the more proximarily situated ones. 



Each testis (PI. 5, figs, i, 2, 6) is spheroidal, pyriform or somewhat 

 irregular in shape. It develops always in relation with those canals on 

 their dorsal side, frequently at the end of a short stalk-like diverticulum 

 arising on the interradial side of the canals. Each is made up for the 

 most part of sexual cells interspersed with a few apparently non-sexual 

 cells. The sexual cells form several compact masses which are marked 

 off rather sharply form one another, much as in ordinary ctenophores. 

 Each mass is separated by a membraneous structure showing several 

 nuclei of a flattened or a vesicular form. 



In a half-mature testis such as figured in PI. 5, fig. 4, various 

 developmental stages of the sexual cell may be met with, the spermatozoa 

 forming the apical part of the testis and the younger elements the basal. 

 The male sexual cells of the earliest stage, the spermatogonia {spg), 

 occur mainly in the basal parts of the testis. The}' are generally oblong 

 in shape and are furnished with a spheroidal or ellipsoidal nucleus in the 

 centre. The nucleus may measure 2-3 11 in diameter and encloses usually 

 one or two nucleoli besides some chromatin granules. The testes of the 

 earliest developmental stage are composed entirely of such cells. Succes- 

 sive developmental stages of the sexual cell up to the spermatozoon 

 could not be followed out. Onl\- a few stages most commonh' met 

 with are shown in PI. 5, fig. 4. In the stage marked spc, the nucleus 

 contains a single chromatin clump in the centre, leaving the peripheral 

 parts quite clear — this apparenth' represents the synapsis stage. Next, 

 in the stage indicated spd, the nucleus is pyriform and shows the 



