DR. T. S. COBBOLD ON SCLEBOSTOMA STNGAMUS. 309 



ing with the line of the upper foui*th of the body. Here the male 

 is usually found rigidly affixed by means of a strong, membranous, 

 sucker-like biu'sa, which proceeds from the lower end of its body. 

 This cup-shaped appendage is formed out of a folded extension of 

 the dermal covering, which thus envelopes the centrally enclosed 

 and rounded tail (fig. 4). The membrane of the bursa is simple, 

 transparent, undivided, smooth at its free border, and strengthened 

 internally by a series of projecting rays, the precise number of 

 which I could not ascertain with certainty. Probably there are 

 twelve ; but I only recognized nine. These rays appear to me to 

 be simple, firm, chitinous bands, whose purpose is to fix and sup- 

 port the bursa, in the same manner as we find the whalebone rods 

 employed to distend the hood of an umbrella. Acting antagonis- 

 tically to these rays we also find a pair of strong retractor muscles, 

 which, taking their origin a little higher up on either side, con- 

 verge below to be inserted into the base of the cup-shaped bursa 

 (fig. 4), In addition to these structures, a very distinct view of 

 the penis can be gained by transmitted light. This organ, in the 

 retracted condition, is entirely concealed within the caudal pro- 

 minence. It is very small, only about the 2-2-5^^ ^^ ^^ i^ch in 

 length, and consists of two narrow cylindrical spicules, which, 

 though distinct, are firmly united at their lower third (fig. 4). 



In regard to the peculiar mode of union of the sexes, it becomes 

 an interesting point to ascertain whether there be an actual incor- 

 poration of the substance of the copulatory organs during or after 

 the act of impregnation. In my specimens none of the three pair 

 were organically united, and I succeeded in separating one pair 

 very readily. Dujardin speaks of them as being soldered together, 

 whilst the statements of Von Siebold are still more explicit. In 

 connexion with this subject, the latter observer makes the follow- 

 ing comment *: — " The two sexes of almost all round worms are 

 united only at the time of copulation. The male of Heteroura andro- 

 phora has also the habit of remaining connected with its mate 

 beyond the period of copulation ; here, thus, there is a continuous 

 union of the two sexes without a growing together ; and in Syn- 

 gamus trachealis there is ultimately a lasting continuity of the 

 sexes by means of an actual growing together." 



Having entire confidence in Von Siebold's statement, I am bound 



to conclude that the sexual union in my specimens had only recently 



been effected ; but, admitting this to have been the case, one 



naturally asks in what manner can the mature eggs make their 



* Wiegmann's Archiv, 1836, p. 106. 



