M. T. Thorell on the Systematic Position of the Argulidse. 277 



here, while the seminal bladder and ductus deferentes lie in the 

 trunk. In the Branchiopods both ovarium and testes have their 

 position in the anterior portion of the tail *. 



While we are on the subject of the sexual conditions of the 

 Argulidse, we must not omit to mention a circumstance which 

 in some measure removes them from the Branchiopoda : propa- 

 gation by means oi parthenogenesis, which seems to be so general 

 in that order, seems to be as rare among the Argulidse as among 

 the Copepoda. 



Among the anatomical characters whereby the Copepoda may 

 pretty constantly be distinguished from the Branchiopoda, it has 

 been asserted, is the absence of gall- secreting branches in the intes- 

 tinal canal. However, according to Claus, many Copepods, 

 especially the genus Sapphirina, possess extremely strongly de- 

 veloped glandular liver-appendages; and since these in many 

 Branchiopoda (as, for instance, the Branchipodidse) are but 

 feebly developed or (as in Limnadia and many Cladocera) alto- 

 gether wanting, we must not attribute to this character any 

 special importance. Still the strong branches of the intestinal 

 canal beneath the head-shield in Apus and Argulus certainly 

 afford further grounds for considering that these creatures are 

 nearly related. 



Neither in the nervous nor circulatory system do I find any 

 characteristics which might contribute to fix the line of demarca- 

 tion between the Branchiopods and Copepods. The copious 

 supply of blood in the head-shield in Argulus, which Zenker 

 regards as attesting the Copepod nature of the Argulidse, 

 depends only on the strong development of this shield, the form 

 of which meanwhile points, as has already been said, to a near 

 relation with the Branchiopoda. According to Leydig and Claus, 

 blood-corpuscles are wanting in the nourishing fluid of the 

 Copepoda, but are found in both Phyllopoda and Cladocera, as 

 also in Argulus. This difi'erence, however, is not constant ; 

 for they are found also, according to Dana, in abundance in the 

 Caligidse in the first-named order. The well-marked separation 

 of the tail from the trunk, and its modification as a respiratory 

 organ, would seem to be the most prominent feature in their 



* Leydig, " Ueber Artemia salina und Branchipus stagnalis, Beitrag zur 

 anatomischen Kenntniss dieser Thiere," Zeitschrift fiir wissenschaftliche 

 Zoologie, Bd. iii. p. 297 &c. Leydig is guilty of a misrepresentation when 

 he says that Joly did not perceive the true ovaria of Artemia salina, but 

 only the uterus, which he mistook for the ovary, Joly expresses himself 

 thus: — "Sur les parties laterales des deux premiers anneaux de I'abdo- 

 men on s'apergoit . . . deux sacs allonges, cylindriques, dont le fond est 

 toume du cote de la queue. Ces deux sacs sont les ovaires proprement dits. 

 lis viennent deboucher dans une matrice ou ovaire extenie, qui parait etre 

 une dilatation considerable de ieur propre membrane." 



