| OCR Text |
Show 338 MR. F. E. BEDDARD ON EARTHWORMS [Apr. 16, P. kilindinensis1. The appearance is very characteristic of those species, and, apparently, of those only. The grooves between the several segments are perfectly distinct. The appearance of this "Pubertiitspolster " is indistinct in the figure (text-fig. 83). I could not find a similar structure in Polytoreutus finni, between which and P. kilindinensis the present species seems to stand. The seta have the usual arrangement which characterizes the genus, i. e. the two seta; of the ventral couples stand apart, while those of the lateral couples are closely paired. As is the case wil h some but not all of the species of this genus, the prostomium does not in the least impinge upon the buccal segment, but is sharply marked off from it by a transverse groove; the prostomium is in fact what Michaelsen has called " prolobisch." There are of course no dorsal pores. The nephridiopores are in front of the lateral couples of seta?. Such are the principal external characters of the present species, which are, \ think, sufficient of themselves to establish its distinctness. In internal characters the members of this genus mainly differ in the form of the spermathecal sacs and of the spermiducal glands. The other viscera are not so variable, unless, indeed, the form of the sperm-sacs in different species is really distinctive of them and not merely due to varying stages of development. I am disposed to think, from my observations upon the present species, that the sperm-sacs do offer characters of some use in discriminating the species of Polytoreutus from each other. In describing Polytoreutus finni2 I drew attention to the extraordinary slenderness of the sperm-sacs, which extend like white threads, hardly, if at all, thicker than the sperm-ducts, for some distance backwards. Michaelsen has by a query suggested that this appearance may be due to immaturity-and a reasonable enough suggestion. And yet I am not altogether disposed to agree with him, since in Polytoreutus hindei I find precisely the same state of affairs. The two sperm-sacs are slender threads which reach back to about the level of the commencement of the spermiducal glands and are swollen here and there like a ganglio-nated nerve-cord. Xow the present specimen is fully mature, as was that of Polytoreutus finni, upon which I founded that species. The probabilities appear to me to be in favour of considering the condition of the sperm-sacs as characteristic of the species aud not to be due to immaturity. However, the question cannot be settled definitely at present. The sperm-duct is very noticeable in the dissection on account of this thickness, which is fully that of the duct leading from the spermathecal sac to the egg-sac. It has a swollen sac at its beginning, as in the other species of the genus. The two spermiducal glands are white thick tubes of some length; they have not the extraordinary thinness and length that characterizes those organs in Polytoreutus finni. Each gland was somewhat bent like an elbow, a feature often shown by these glands in 1 See Beddard, P.Z. S. 1901, vol. i. text-fig. 50, p. 188, and text-fig. 51, p. 190. 2 " A Contribution to our Knowledge of the Oligochajta of Tropical Eastern Africa," Quart. Journ. Micr. Sci. xxxvi. p. 241. |
