OLIGOCHABTA. 



503 



in 12 in Pontoscolex and Gcoscolcx. In Brachyilrilus the ovaries are said to be in 

 12, but this is doubtful. 



The reproductive glands are definitely localised thickenings of the 

 coelomic epithelium, and are placed upon the posterior faces of certain 

 septa. The part of the body-cavity in which the testes lie may, in 

 some Terricolae, be cut off from the rest by a development of the 

 septa which forms the median part of the vesicula seminalis or 

 sperm reservoir (Figs. 412, 413). 



The vesiculae seminales or sjwm sacs are developments of the 

 septa of the testes segments. They are paired structures in Terri- 

 colae, and unpaired in most Limicolae. They communicate with the 

 coelom, but in many Terricolae the part of the coelom into which they 

 open is, as stated above, cut off from the rest by a membrane which 



xi sb xn xm xiv 



FIG. 413. Diagram of a longitudinal 'section through the generative segments of Lumbricus 

 herculetts to show the. relation of the generative ducts and sperm sacs, etc. The segments 

 are numbered in ruinan numerals, eh ovisac ; ep ectoderm ; ct internal opening of oviduct ; 

 h testes ; Im longitudinal muscles ; ov ovary ; rm circular muscles ; rs spermathecae ; sl> sperm 

 sacs; sk sperm reservoir; st sperm rosette (internal opening of vas deferens) in the sperm 

 reservoir. (After Hesse.) 



encloses a space containing the testes and the sperm rosette. This 

 is the sperm reservoir (Fig. 413). A sperm reservoir is not developed 

 in Allolobophora, Acantlwdrilus, and some other forms (Fig. 414). 

 Sperm sacs are absent in the Encliytraeidae (except Mesenchytraeus). 



The vesiculae seminales or sperm sacs do not necessarily correspond 

 in number with the testes ; they vary in number from one pair to 

 four (Fig. 414). They may attain a great size, extending back 

 through a great number of segments (60 in a species of Geoscolex). In 

 the Limicolae the sperm sac is, as stated above, generally unpaired. 



A similar sac is formed in connection with the ovary in some 

 forms. This ovisac in the Limicolae is unpaired, and may be very 



