Physiology 0/*Ha3matopinus tenuirostris, Barm. 95 



upon this single character. A rational classification must be 

 founded upon other equally important characters, such as espe- 

 cially the buccal organs, but not only their external structure, 

 as we already distinguish litfe with suctorial from those with 

 biting buccal organs, but also the internal constitution of the 

 organs in question. 



The above-mentioned bilocular ovarian tubes are connected 

 with the uterus by shorter or longer tubce. The average 

 length of these tubce amounts to # 058 millim., while the 

 greatest observed by me was % 176 millim. According to 

 the development of the ova contained in them the ovarian 

 tubes present a difference of size and thickness. The lower 

 chamber, nearest to the uterus, is always the largest. In it a 

 single egg attains its development. As soon as this has 

 become mature it is expelled. Then the walls of this chamber 

 shorten, by which the second or upper chamber is brought 

 nearer to the uterus. It is only then that the ovule in this 

 chamber can become developed to its maturity. Thus we 

 find the view expressed by Landois (24, p. 51) confirmed in 

 this case also : — Ci The ova arrive at their full development in 

 the chamber in which they are placed at first ; they do not 

 pass into the immediately underlying emptied chamber in 

 order to become developed." When the ovum has attained 

 its full maturity in the second chamber and been expelled 

 therefrom, the course of development has come to an end in 

 that ovarian tube. In this way the Sharp-headed Ox-louse, 

 if it does not perish previously, may deposit twenty eggs. In 

 connexion with this it is to be remarked that in the same 

 individual several eggs may arrive at maturity at the same 

 time, and these are then expelled soon after one another. 

 Most frequently I found in each ovary one ovum approaching 

 maturity ; but the presence of two in the same ovary was not 

 a rarity. In the latter case, however, the other ovary had 

 only one ovum in an advanced state of development. Indeed 

 more than three would not find room in the body-cavity ; for 

 a single mature ovum fills nearly one fourth of the abdomen. 

 As regards the size of the different chambers, this is very 

 variable in the case of the lower one, according to the stage 

 of development of the ova, while in the upper one it is more 

 constant. Thus the length of the lower chamber varies from 

 O509 to 0-929 millim., and its width from O092 to 0'396 

 millim. The second chamber, on the contrary, which is sepa- 

 rated from the former only by a constriction, is 0*156 millim. 

 long and 0049 millim. wide. It is continued upwards into 

 a tubular structure of 0078 millim. length (fig. 11 c), which 

 unites with the analogous vessels of the other ovarian tubes of 



