GENERATIVE SYSTEM. 87 



noticed the sac in Lineus, does not mention more than " fossettes cephaliques " in this 

 group. 



11. Generative System. 



In the majority of the Enopla the sexes are separate, the only known exceptions being the 

 Borlasia hermaphroditica of Keferstein, and the Borlasia Kefersteinii of Marion. The genera- 

 tive products are developed between the inner muscular layer of each lateral region of the body 

 and the glandular digestive cavity, and enclosed in special spaces (Plate XVI, fig. 13) formed by 

 transparent membranous sacs («?), which are connected with the inner muscular layer of the body- 

 wall (Plate XVI, fig. 2,/). The contents are evacuated by pores above the lateral nerve-trunks, 

 which (pores) are very distinct immediately after the issue of the ova or spermatozoa. 



a. Male Organs. 



The sperm-sacs in the male (Plate XVI, fig. 5, e) generally present a pyriform or flask-shaped 

 aspect, especially in the early stages, being attached to the body-wall by a narrow tubular 

 neck, which at the proper period doubtless gives transit to the contents of the sac. In the early 

 condition the latter is minutely granular, then cell ulo- granular ; and in the mature state it has a 

 finely fibrous or streaked appearance from the spermatozoa. 1 Sometimes both granules 

 (Plate XIV, fig. 17) and spermatozoa occur in the same sac, and then the former are often 

 observed to be somewhat regularly arranged (Plate XIV, fig. 16). The spermatozoa in A. lacti- 

 floreus (Plate XIV, fig. 18) have a slight curve of the body, which gently widens from the tip 

 and ends in a perceptibly larger rounded knob, to which the long tail is attached. The mature 

 males are easily distinguished from the females by their whitish or pinkish aspect, and their 

 bodies are less distended. The spermatozoa of N. gracilis (Plate XVII, fig. 8) are most active 

 wriggling structures, of a more slender shape than those of A. lactifloreus or Tetrastemma (Plate XVI, 

 fig. 7), appearing under a power of 1000 diameters as simple rods, slightly larger towards the 

 end from which the elongated and very fine tail proceeds. 2 The sperm-sacs are very numerous in 

 N. carcinophila ; but the tenuity of the spermatozoa (Plate XVII, fig. 9) renders their exact 

 structure somewhat obscure. The body of the spermatozoon is elongated, gently curved, and 

 slightly thickened at the end to which the filament is fixed. It is very common, moreover, to 

 observe one or more minute clear globules attached to the spermatozoon, so that the structure 

 seems to have a tail at both ends, or a flattened head. These appearances have misled even so 

 experienced an observer as M. van Beneden, who figures the organs as possessed of a some- 

 what globular body, with a filament at each pole. But, independently of the strange exception 

 which such a condition would make in Nemertean physiology, the frequent occurrence of more 



1 This peculiar striation resulting from the arrangement of the spermatozoa has been seen in other 

 groups of the animal kingdom, vide Allman, ( Gymnoblastic or Tubnlarian Hydroids/ p. 65, f. 31, C, 

 and Biitschli, < Zeitsch. w. Zool./ Bd. xxi, 4. 



2 Prof. Huxley finds the filament also attached to the broader end in the Hydrozoa. 



