EEPORT ON THE NEMERTEA. 47 



system increases with age ; there thus might remain one chance that the New Zealand 

 specimen of Cerebratulus macroren could still be assigned to Cerebratulus parkeri, if 

 we assume that increase in growth can have brought about a further extension backwards 

 of the principal nephridial duct, and at the same time the appearance of a second deferent 

 duct immediately behind the first. For the present this assumption appears to me to be 

 more strained than my own, which unites the New Zealand and the Japanese specimens 

 by laying more stress upon the large size of the longitudinal tube, combined with the 

 terminal situation of the deferent duct. 



The further peculiarities that reveal themselves on studying the microscopic sections, 

 certainly show that the tw^o species, Cerebratulus macroren and Cerebratulus parhen, 

 cannot be very far apart. Both have in common the very thick and homogeneous secondary 

 basement layer beneath the outer glandular layer of the integument (PL XL fig. 11). 



It would also be difiicult to point out salient points of disagreement in the muscular 

 body-wall, the proboscidian sheath, and the proboscis which would hold good when 

 respectively comparing the head, the oesophageal, or the posterior body region. 



Cerebratulus, sp. inc. (PI. X. fig. 7; PL XV. figs. 6-8, 18.) 



At the close of our systematic description of the Schizonemertea I must mention 

 certain fragmentary specimens, which have all the aspect of belonging to distinct species, 

 but which I cannot venture definitely to unite with any of the species here described, or 

 with such as have been published elsewhere. The fragments here aUuded to are mostly 

 without a head, and some of them of not inconsiderable size. I wUl discuss them in the 

 order of the stations at which they were obtained. 



The first was procured in the Kerguelen waters. It is important, in consequence of 

 peculiarities in its integument, which will be more fully discussed in the paragraph devoted 

 to this system. A part of a section was figured on PL X. fig. 7, and from that section it 

 may also be gathered that the dorso-median medullary nerve is comparatively very massive. 

 This might eventually prove that it was related to Cerebratulus medullatus ; the difi'er- 

 ence in the integument, "though important from a morphological point of view, hardly 

 justifying the establishment of a diff"erent species, supposing all the other characters, 

 external and internal, might prove to be identical. That diff"erence might then be con- 

 sidered as indicative of a variety. 



The second Cerebratulus, about which I must remain in doubt, was obtained among 

 the Philippine Islands (ofi" Zebu). MTntosh has made the following notes about 

 these fragments : — " Fragments of a large species. The fragments in all measure over 



100 mm., with a diameter of 12 mm. at the widest part The carrying of 



the vascular trunks far inwards towards the ventral middle line seems to be a feature 

 . in this form." 



