146 DR. J. STEPHENSOX ON THE MORPHOLOGY, CLASSIFICATION, 



found a number of cases where there were additional female 

 pores one segment behind the normal, and where therefore there 

 were probably additional ovaries and oviducts internally to 

 correspond. 



The testes which we suppose to have disappefired from 

 segment xii also sometimes crop up again. Thus Woodward (28) 

 found testes here in three cases out of fifty examined. Beddard 

 (4) found a pair of testes in segment xii in Fontoscolex corethrurus 

 (in this case the gonads of segment xiii also appeared to be 

 testes). 



On the other hand, the gonads of segment xii, which ought, 

 when they reappear (if the common ancestor of earthworms was 

 constituted as above supposed), to be testes, ai'e when present 

 sometimes ovaries. Beddard (I. c.) found this to be so in some 

 examples of Fontoscolex ; it is so (if we may draw conclusions 

 from the position of the female pores) in some specimens of 

 Perionyx excavatus (Beddard, Z.c); and Woodward had six cases 

 of this condition out of the fifty specimens of British earthworms 

 Avhich he examined. 



In a number of cases the nature of the gonad in segment xii 

 is indeterminable, or the evidence is inconclusive. Beddard 

 {I. c.) believes that the same gland in Fontoscolex may produce 

 either ova or spermatozoa. In one specimen examined micro- 

 scopically by Woodward the gland was actually hermaphrodite. 

 In three very young specimens (? of Lumbricns ritbellus) a gonad 

 was present on each side in segment xii, but at that stage could 

 not be identified as definitely testis or ovary (Woodward suggests 

 that this pair is always developed in the embryo). Beddard 

 (5, 8) found this pair of glands present in embryos of Octochcetus 

 vmltiporus, but of course could not identify it, at that stage, as 

 either testis or ovary. Beddard also notes (9) that two pairs of 

 ovisacs have been found both by Horst and himself in certain 

 species of Perichsetidfe, in segments xiii and xiv ; these would 

 correspond to ovaries in xii and xiii ; Beddard remarks on 

 certain resemblances of these organs to sperm-sacs, and, since 

 neither gonads were found in segment xii nor ova in the corre- 

 sponding sacs, it seems not improbable that the organs in 

 segment xiii were vestigial sperm-sacs, and the gonads which 

 formerly existed in segment xii were testes. 



There is thus no doubt that ovaries occur not infrequently at 

 the present day in segment xiv, and that segment xii also 

 frequently contains a pair of gonads, which in some cases are 

 ovaries, in some cases testes, and in some cases their nature is 

 equivocal. According to our view they were, in the ancestral 

 eai^th worms, regularly testes. 



The more usual view of the origin of the terrestrial Oligochaeta 

 (Beddard, 9; Michaelsen, 12, 17) is rather different. The 

 Phreoryctida?, with two pairs of testes and two pairs of ovaries, in 



