1892.] SPECIES OF EARTHWORMS. 695 



the large egg-sacs. Even Rosa, who is so anxious to minimize the 

 affinities of the Moniligastridse to the lower Oligochfeta, admits 

 that the size of the eggs-sacs is unknown in the Terricolae, though 

 it is, he remarked, going rather too far to exclude Moniligaster 

 from the Terricolse on these grounds. In Moniligastei- heddardi no 

 egg-sacs were found by Rosa ; but I do not think that this failure 

 to find the structure in question is tantamount to a proof tliat they 

 are non-existent in that species, as Rosa seems to imply. Anyhow 

 they are large in tlie present species, and occupy at least three 

 segments. Bourne, the first to discover these bodies, stated that 

 they occupy in Moniligaster minutus segments xii.-xv. As to the 

 ova of Moniligaster, Bourne says nothing about them save that 

 there are ova in these sacs ; the eggs in Moniligaster beddardi are, 

 according to Rosa, very minute. In the species here under consider- 

 ation the ova present a very remarkable character, unique among 

 Earthworms : they are not particularly large, though, perhaps, 

 larger than in many Earthworms ; the remarkable fact about them 

 is that they are crowded with yolk-particles : to so great an e.\.tent 

 is the yolk developed that the nucleus is by no means always 

 apparent ; the yolk-particles are moreover, as is shown in the accom- 

 panying figure (Plate XLV. fig. 1), of considerable size, quite as 

 large as they are in eggs of a much greater size. This fact about 

 the ova of Moniligaster bahamensis is of considerable interest. I 

 pointed out some time since' that the only distinguishing characters 

 between the Megadrili and the Microdrili of Benham^ not alluded 

 to by Benham himself, are the three following: — 



(1) Large size of ov;i. 



(2) Clitellum consisting of only a single layer of cells. 



(3) Sexual maturity at a fixed period. 



In the three points mentioned the Microdrili (= Limicolse of 

 Claparede minus Naids and Molosoma) differ from all the Megadrili or 

 Earthworms. Now I have just pointed out that the ova of Monili- 

 gaster, although not so large as they are in the Microdrili, agree 

 with them in having a great quantity of yolk, a character not found 

 in any other Earthworm ; this is, at any rate, an indication of a step 

 in the direction of the Microdrili, even if it be not held to be a 

 point of close affinity with them. On a previous page I have pointed 

 out that the structure of the clitellum is quite like that of the lower 

 Oligochseta in being made up of a single layer of epithelium only ; it 

 may be added that in all possibility the sexual maturity is at a fixed 

 period ; this would account for the failure of so many investigators 

 to find the clitellum ; Prof. Bourne tells me that he expects that 

 the clitellum will be found at the proper season in all Moniligasters. 



It is difficult therefore to see on what grounds Moniligaster is to 

 be referred to the Earthworms as opposed to various groups of the 

 aquatic Oligochgeta. Rosa justly points out that Tetragonurus 



^ " On the Anatomy of Ocnerodrilus (Eisen)," Trans. Eoy. See. Edinb. vol. 

 XXX vi. 



^ " An Attempt to Classify Earthworms," Q. J. M. S, vol. xxxi. 



