270 



HA RD Wl CKE'S SCIENCE- G OS SIP. 



of the bladders when microscopally examined were 

 found to be filled with dense masses of matter 

 containing protoplasm. Plants kept in a purer 

 condition were sickly and much paler in colour, the 

 quadrifid processes being decidedly less dense in 

 their contents. 



J. H. A. Hicks, F.R.H.S. 



THE DORSAL PORES OF EARTHWORMS. 



By the Rev. Hilderic Friend, F.L.S., Author of 

 "Flowers and Flower-Lore," etc. 



IF a specimen of the common earthworm is 

 examined, especially after having been pre- 

 served for a time in spirits, it will be found that a 

 number of pores exist on the back. They are most 

 readily seen on the girdle as a rule, and look exactly 

 like the holes which result from the puncture of a pin 

 or needle. These openings have been known for a 

 considerable time as the dorsal pores, a name which 

 serves not only to define their position, but also to 

 differerftiate them from the other openings which 

 exist on various portions of the worm's body — such as 

 the male or spermiducal pores, the nephridiopores, 

 and the puberty pores {tubcrcula pubertatis). 



It is now many years since these apertures were 

 first detected. Who first observed them, it is 

 impossible to say. Equally difficult would it be to 

 decide who was the first to notice their presence in 

 describing the animals. In 1727 Dr. Derham, Canon 

 ( of Windsor, wrote a very interesting work, entitled 

 Physico- Theology, in which he endeavours to demon- 

 strate " the being and attributes of God from His works 

 of Creation." He says that under the skin of worms 

 there lies a slimy juice, that they emit as occasion is, 

 at certain perforations between the annuli, to lubricate 

 the body, and facilitate their passage into the earth.' 

 A little later, however, he shows that a certain Dr. 

 Willis had previously written an account of these 

 " Foramina on the top of the back, adjoining to each 

 ring, supplying the place of lungs." Now Willis 

 published his work, Dc Aiiima Brutorum, in 1672, so 

 that for upwards of two hundred years the pores have 

 been known to science, to go no further back. It is 

 only in recent years, however, that they have been 

 carefully noted, and the position of the first pore 

 recorded for the different species of worm. It has 

 been thought by some that the first dorsal pore was so 

 uniformly placed in the various species of earthworms 

 that a specific character might be based thereon. 

 This, I am disposed to think, ^is not borne out by 

 facts. 



Dr. Benham, one of our few English authorities on 

 the subject, says : " In many earthworms the cctlom 

 is put into communication with the exterior by means 

 of a series of dorsal pores, placed on the intersegmental 

 grooves. In Lumbricus these pores occur in every 

 somite after about segment viii. In Digaster and 



Perionyx they commence just behind somite iv., in 

 Plutellus behind somite vi. In Pleurochaita and 

 Typhrcus the pores are present only behind the 

 clitellum. They are present in Acanthodrilus, and in 

 many Perichsetse. " In Allurus they begin behind 

 segment iii. or iv. 



As will be inferred from the foregoing, a variety of 

 ideas have prevailed respecting the use to which these 

 apertures were devoted in worm economy. Willis 

 says they supply the place of lungs, and if Derham's 

 remarks apply to the dorsal pores, he regards them 

 simply as the openings through which lubricants were 

 poured. Lloyd Morgan is as cautious on the subject 

 as he is inaccurate. He says : " Every segment of 

 the body, except the first, has a dorsal pore opening 

 into the anterior part of the ring in the mid-dorsal 

 line, and two very minute pores, one on each side of 

 the ventral line, which are the external orifices of the 

 nephridia or segmental organs, whose function is 

 excretory." The dorsal pores are not found in the 

 typical earthworm :on every segment save the first, 

 and if they are, we are not favoured by the professor 

 with a vestige of an idea as to their use. He says : 

 " There are no specially differentiated respiratory 

 organs, respiration being apparently effected by the 

 surface of the body," so that he does not regard the 

 dorsal pores as lungs. 



The most important contribution to the subject is 

 undoubtedly that which was made a few years ago by 

 Hermann Uhde, in a paper which deals chiefly with 

 the structure of the body- wall in earthworms.* He 

 points out that "the dorsal pore lies on the anterior 

 edge of the segment in which it occurs, and appears 

 on the intersegmental groove. It is absent from the 

 foremost segments, but the position of the first pore is 

 constant for a given species. In the common earth- 

 worm it occurs between viii. and ix., and in the 

 turgid worm between x. and xi." Claparade 

 formerly described the epidermis as being folded 

 inwards at the dorsal pore, just as it is where the setce 

 are situated, but Uhde shows that such is not the 

 case. By stripping off the epidermis I have been able 

 to detect the infolding of the cuticle around the setae, 

 but not around the dorsal pore, which, as Uhde 

 affirms, is a perforation through the epidermis and 

 the muscular layers. The pore appears, according to 

 Vejdovsky and others, to be wanting in fresh-water 

 worms or Limicok^. In some worms, when the 

 girdle is fully developed, the pores become closed 

 through the growing up of the cuticle around the 

 edge. This is not always the case, however, for the 

 mucous worm has been noted by some to be an 

 exception, while I have found that the dorsal pore on 

 the clitellum or girdle of some species is quite as 

 discernible after the organ has attained full develop- 

 ment as before. 



* "Zeit. f. Wiss. Zool.," xlvi. pp. 85-142. Benham, "Q. J. 

 INIic. Soc," Aug. 1886, No. cv., pp. 102-4. 



