46 THE YQYAGE OF H.M.S. CHALLENGER. 



The sack of Balanus tintinnabulum was studied in transverse sections ; its diameter was 

 about 0'9 mm. I Have beeri unable to investigate the way in which the oviduct 

 communicates with it. 



If Kossmann's explanation as to the presence of the irregular mass in the interior of the 

 curious sack at the end of the oviduct be right (and I have no sufficient ground to doubt 

 its correctness), the function of the cells which form the wall of the sack is to produce a 

 viscous fluid which envelops the eggs. The thick mass which sometimes, and even very 

 often or as a rule, is found in the interior of the sack is formed because the secretion 

 continues incessantly, even when no eggs pass through the oviduct. The quantity of this 

 viscous fluid which is secreted by these cells must indeed be rather large ; for when a 

 Lepas is furnished with ovigerous lamellse and the interior of its sacks studied, large 

 masses of the secreted substance are present. This must necessarily have been formed 

 after the eggs passed through it, and cannot have been very long before, as in the 

 Cirripedia the evolution of the eggs in general does not take long. The very regular 

 shape of the mass in some genera, as e.g. in Leilas, where it is shoe-shaped and has 

 a very smooth surface, must be ascribed to its being modelled, at least in part, after the 

 internal surface of the sack ; it remains, however, in my eyes a curious fact which, 

 perhaps, has an analogy in the presence of a chitinous bag within the stomach in this 

 same group of Cirripedia. I observed it in the stomach of all the Cirripedia of which I 

 prepared transverse sections ; according to Darwin it is a model of the stomach, filled 

 with excrement and expelled by the rectum entirely in a single piece, as he observed in 

 some living specimens of Balanus halanoides. 



To understand the physiological meaning of the apparatus at the en-d of the oviducts, 

 a second difficulty arises from the circumstance that we do not know the place where, and 

 the way in which, the eggs are fecundated. If Kossmann's supposition be correct, the 

 „eggs are evacuated after being united together by means of the fluid secreted by the 

 cells of the curious sack. These eggs, however, are ovarian, not yet fecundated eggs ! 

 I think it is difficult to understand how they are fecundated after they are united together 

 by a fluid viscous glue. Of course, the only way of investigating successfully physio- 

 logical questions of this kind is to study fresh and living material. But this study can 

 only give trustworthy results when the anatomical structure is sufficiently well known. 

 I think I have contributed to a more accurate knowledge of the anatomical structure. 



I will not take leave of this subject without pointing out the great probability 

 that the apparatus at the end of the oviduct morphologically represents a second seg- 

 mental organ. Krohn ^ has already shown that, of all Crustaceans, the female genital 

 openings are placed nearest to the cej^halic part of the body in the Cirripedia ; and even 

 at present, though our knowledge of Crustaceans has been considerably increased since 

 the year 1859, it is still true that they are the only Crustaceans which show this 



' hoc. cit, p. 360, note at the foot of the page. 



