50 NATURAL SCIENCE. July. 



of the group. First among recent publications stands the monumental 

 work of Vejdovsky (15) upon the embryology of Rhynchehnis and 

 Ltinihricus. One of his most important results is a clearing up of the 

 very complicated series of excretory organs which arise at different 

 times in the embryo. The first organ which serves this purpose is a 

 series of tubes excavated in the interior of certain epiblast cells at 

 the gastrula stage or even before ; these cells are traversed by clear 

 tubes which open behind into the primitive body cavity, i.e., the space 

 between the epiblast and the hypoblast. Next there is in some forms 

 a pair of long tubes which open on to the exterior in the head region ; 

 these are the ciliated larval pronephridia, and they seem to be 

 developed out of, or at least to have some connection with, the last- 

 mentioned larval excretory cells. Quite independent of the last are 

 the embryonal pronephridia ; these organs are a series of paired tubes 

 which open into the body-cavity by a " flame-cell." The flame-cell 

 becomes a ciliated funnel, the nephridium grows, and we have the 

 permanent nephridium of the adult. To give a thorough account of 

 Vejdovsky's great book would take up more space than we can give ; 

 but one other point of some importance must be mentioned. He 

 found that in the young Lumhvicus the vascular system consists of 

 a dorsal and of a ventral vessel which are connected by circum- 

 intestinal vessels in each segment of the body ; the dorsal vessel, as 

 Vejdovsky himself was the first to discover a good many years ago, 

 is at first double, a state of affairs which is permanently retained in a 

 considerable number of earthworms throughout life. The connection 

 of the dorsal and ventral vessels by a series of similar tubes in all the 

 segments of the body is precisely what is met with in the simpler 

 forms of Oligochaeta such as the Tubificidae. As still further 

 tending to show that this is the primitive arrangement in worms 

 which no longer show it, I may mention Bourne's discovery (11) that 

 in Pavanais the young buds have a full complement of these commis- 

 sural vessels which are largely wanting in the adult. 



Recent investigations into the anatomy of that very remarkable 

 family the Eudrilida^ have progressed so considerably during the last 

 few years, that from being one of the least known they have become 

 quite one of the best known groups of Oligochaeta. They have been 

 referred to above as suggesting a link in the direction of the Hirudinea. 

 Other points of interest have arisen. The most marked character of 

 the family is the presence of large, usually unpaired, sacs which open 

 on to the exterior and generally contain sperm. For this reason they 

 have been called spermathecae, though their anatomical structure is 

 not precisely that of the spermathecae of other earthworms. The 

 investigations of Rosa (9) and myself (4) appear to have put beyond 

 a doubt that these large sperm-holding sacs are derivatives of the 

 septa which acquire an external pore ; they can, therefore, have no 

 morphological relationship to the spermathecae of, say, Lumhvicus, 

 though an intimate physiological relation. But the interesting point 



