REPORT ON THE NEMERTEA. 119 



in the second of the two propositions above enumerated. At the same time we find the 

 spot where the pore will appear indicated by a pointed projection of the sac between the 

 muscles, and it is a fact very worthy of notice that the more we approach this preformed 

 outward duct, the less ripe are the ova (PI. XV. fig. 14). The same fact is noticed in 

 many other Nemertea ; Pelagonemertes even shows traces of it (PI. VIII. fig, 8, ov.) In 

 Carinella I found it persisting even after the definite pore is established, and the most 

 plausible explanation appears to me to be this, that the deeper inwards the developing 

 generative products are situated, the more they are surrounded by the gelatinous tissue, 

 and the better their conditions of nutrition must be ; whereas those which are observed 

 close to the duct, piercing the muscles, wdl only gradually increase in size, when in 

 their turn similar favourable conditions are offered to them. 



The fact of the occurrence of definite preformed ducts without pores was observed 

 by me in Amphiporus moseleyi, Amphipoms marioni, Drepanophorus lankesteri, and 

 Drepanophorus serraticollis, and of several of these I also had ripe specimens, in which the 

 fact could be determined that it is, indeed, in the places where these pointed projections 

 are found that the pores afterwards appear (PL IX. figs. 5, 6). 



In this place I may mention that according to embryological observations (XIV) the 

 generative sacs are primitively in connection, at least in the species investigated, with the 

 epiblast by means of a strand of tissue which is not indicative of the ultimate duct. 

 These strands, however, are situated on the other side of the nerve-stem, and thus are in 

 no way identical with the projections which were here described and discussed as preced- 

 ing the definite generative pores. 



The duct which pierces the muscles to afford a passage to the generative products is 

 generally shortened as maturity advances, through the distension of the body by the 

 ripening of ova or spermatozoa, and the consequent decrease in thickness of the mus- 

 cular body-wall. Still, in Cerebratulus macroren this duct presented an uncommon 

 feature, which must here be mentioned, and which is figured on PI. XV. fig. 19. After 

 having pierced the circular muscular layer /3, it distends in the layer 7 to a second 

 sac-like expansion, which in its turn communicates with the exterior by a small opening. 

 This was not a local disturbance, but was met with in very numerous generative ducts, 

 both on the right and left sides of the animal. 



In Eupolia and Schizonemertea the ripening sacs, developing in pairs between each 

 successive pair of intestinal caeca, are often wedge-shaped, with the sharp edge turned 

 outwards, and the broad end between the two intestinal caeca, where these emerge from 

 the principal longitudinal cavity of the intestine (see woodcut fig. 6, p. 120). And, in 

 addition to this, another fact is very marked in Eupolia giardii, viz., that dorsally 

 and ventrally the generative casca become lobulated or arborescent, sending out short 

 lobes of indented and irregular shape. 



It would, however, lead us too far, and hardly offer any additional interest, to discuss 



