120 Descriptions of Preparations. 



segment sixth in order anteriorly to the clitellus. In this pro- 

 minence there is no foramen, but two spines modified so as to 

 co-operate with the clitellus as an organ of adhesion in the act 

 of copulation may be observed to be implanted in it. These 

 spines belong to the inner series of locomotor spines, which are 

 prolonged from the third or fourth or fifth segment of the body 

 anteriorly, down to the posterior segments, upon the last of which 

 they, as well as the spines of the outer series, fail to be developed. 

 The outer row of spines is very visible along the line where the 

 darker coloured dorsal region shades oif into the lighter coloured 

 ventral. Each series is represented in the Lumbricidae by two 

 spines only; the multiple or fasciculate arrangement not being 

 found in this family, which are therefore pre-eminently 'oligo- 

 chaetous.-' The external series is wanting not rarely upon the 

 anterior segments, and may be wanting even as far back as the 

 cHtellus inclusively. The spines of the inner series are modified 

 so as to subserve the mutual adhesion of the allotriandrous Lum- 

 bricus in the act of copulation, not only in the segment already 

 specified, but also in the entire series of segments occupied by the 

 clitellus, and in the tenth and fifteenth segments, where they are 

 thinner and twice as long as in other segments. The oviducts 

 and the vasa deferentia open in the fourteenth and fifteenth seg- 

 ments respectively, just externally to the outer of the two setae of 

 the inner row. In large specimens of Lumbricus communis, an 

 orifice may often be noted in the median dorsal line, in the inter- 

 space between the rings from the tenth segment or so backwards. 

 From this orifice, which opens into the interior of the posterior of 

 the two segments between which it is placed, in a recently killed 

 animal, the peri-gastric fluid may be seen to escape in small jets 

 upon pressure. Much variety is observable in the condition of 

 development of the clitellus, and even the number of segments 

 composing it and inteqiosed between it and the head are by no 

 means uniform within the limits of the same species. 



For the zoological characters of the family Lumbricidae, see British 

 Museum Catalogue of the British Non-parasitical Worms, by 

 George Johnston, M.D., 1865, pp. 57, 318, and especially 

 p. 323 for the variability in external anatomy just mentioned. 



For the anatomy of Lumbricus, see E. Ray Lankester, Esq., Quar- 



