30 BULLETIN OF THE 



Lang ('81, p. 79) speaks of a "Zellenbeleg von wirklichen Ganglien- 

 zellen " around the brain of Triclads. lijima ('87, p. 353) describes these 

 cells as being unipolar with extremely delicate processes. I also find a 

 layer of closely packed cells with large nuclei around the brain, more 

 especially about the so called sensory portions (Plate III. Figs. 26-31, 

 Plate IV. Figs. 39 and 40), but I cannot say that these are ganglionic 

 cells. They resemble in every way connective-tissue cells ; they react 

 like them with stains, and are more prominent only on account of their 

 compact arrangement. The nuclei of the two large " Substanzinseln " in 

 the lateral m^isses of the brain (Plate 111. Figs. 28, 33, Plate IV. Fig. 39, 

 con't. lis.) are both identical and continuous with the nuclei surrounding 

 the brain, and those found in the main nerve trunks cannot be distin- 

 guished from them. The ganglionic cells occurring in the nerve tissue 

 are not as large, nor do their nuclei stain as deeply, as those occurring 

 around the brain mass. I therefore believe that the latter belong to the 

 mesenchyma, and that the " Substanzinseln " are only intrusive con- 

 nective tissue.^ Aside from this, I can add nothing to the observations 

 of lijima on the finer structure of the nervous tissue. The longitudinal 

 nerve trunks in some places appear to be double for a considerable dis- 

 tance, being split, as it were, by the ingrowth of mesenchymatous tissue 

 (Plate III. Figs. 33 to 36, and Plate IV. Fig. 38). All such openings, 

 as pointed out by Lang ('81, p. 56), occur between the points of origin 

 of the lateral nerves. 



The testes are numerous, and are found lying close together through- 

 out the whole length of the animal. Their development takes place 

 before that of the yolk glands. While the latter are still in an early 

 stage of development, spermatogenesis has been completed, the testes 

 have disappeared, and the spermatozoa are found filling the vasa def- 

 erentia. The testes first appear as spherical clusters of cells, which 

 by division increase in number and arrange themselves in the form 

 of hollow spheres. Some of the peripheral cells divide rapidly into 

 small spherical cells, that come to lie in the cavity of the testis. These 

 cells become elongated or pear-shaped, and are then differentiated into 

 two portions, a deeply stainable thickened end, and a tapering tail por- 

 tion (Plate II. Fig. 24). Further elongation takes place, until the form 



1 Since I came to these conclusions in regard to the mesenchymatous character 

 of the so called " Substanzinseln," I have been gratified to learn that my conclusions 

 agree with those of Loman ('87, p. 77). In Bipalium, then, as well as in Phago- 

 cata, the " Substanzinseln " present in all particulars the same differences from 

 ganglionic cells. 



