224 DE. W. B. BENHAM ON 



in the paper under review, does note these variations, and makes 

 " subspecies " for what other zoologists, if they had not had a 

 series of specimens to examine, would have termed " new 

 species." "With regard, again, to the position of the spermiducal 

 gland and the gizzard. These organs usually appear to occupy 

 more than one segment, but how many segments — if more than 

 one — are morphologically occupied by them is unknown. It 

 appears to me, from my own observations, that each belongs to 

 a single segment — the gizzard to the 8th (as E-osa has suggested), 

 the spermiducal gland to the 18th, — but that each may push the 

 septa limiting the segment backwards and forwards or in both 

 directions. And when we state in a description that the spermi- 

 ducal gland " occupies three segments," we do so with an idea 

 of conveying the relative size of the organ, and do not intend — 

 as Michaelsen appears to think — to convey the idea that it lelongs 

 morphologically to these segments. Certain things are postulates 

 of the genus : this is one. 



This organ, too, is liable to variation, as I myself have pointed 

 out {I. c. p. 43). Again it becomes most necessary to have really 

 careful description and figures of the organ ; for there is probably 

 a very fair constancy in the general characteristic appearance of 

 the gland, which is more readily expressed by a figure than in 

 words. The minuter lobulation of course varies, but in some species 

 it is very much more extensive than in others ; and this is too 

 often expressed by vague terms, such as " compact " or " loosish," 

 without even a statement as to the general outline of the gland, 

 which I still believe, in spite of slight variations, to retain its 

 character. It appears to me, in view of the great number of 

 species in the genus Perichoeta, that the time has come to insist 

 on these matters. Comparison of "new species" with old ones, 

 and of individuals of the same species with one another, will, I 

 doubt not, reduce the aggregate number of species as more 

 specimens are carefully examined. 



EXPLANATION OF THE PLATES. 

 Plate 15. 

 Fig. 1. Perichmta nova hritanniccB, n. sp. 



Fig. 1 a. View of the male pores and copulatory structures, s. Anterior sucker- 

 like organ, s'. Posterior sucker-like organ limiting the " porophore," 

 ■which bears the male pore ( c? ). -p. One of the copulatory papillas, of 

 which there is one each side of each pore. 

 Fig. 1 h. Spermiducal gland. X 4. d. Penial duct. 



