PROTEOLEPAS BIVINCTA. 603 



little anteriorly to the prosoma, or second thoracic segment.* 

 From what is actually seen in the complemental male of 

 Scalpellum Peronii, and from what may be inferred from the 

 structure of these parts in the pupae of all cirripedes, there 

 can be no doubt that if the ovarian caeca were in any case 

 not developed, the cement-ducts would enter the body at the 

 spot where the two simple ovarian tubes, which serve to unite 

 the ovarian caeca with the true ovaria, do enter. Now if we 

 look at the drawing (PL 25, fig. 7) of Proteolepas, we shall 

 see that the cement-ducts enter the body at a medio-dorsal 

 point, a little anteriorly to the second thoracic segment, and 

 therefore in the normal position. 



Secondly : the external . membrane of the two threads, 

 investing the two cement-ducts, it should be remembered, is 

 not moulted, and is added to during growth (being lined 

 internally by corium), only round the upper, collar-like edge. 



Thirdly : the external covering or carapace of every young 

 cirripede, at the period of its metamorphosis, enters, at its 

 lower end, the cemented antennae, in the form of two short 

 tubular prolongations, by which alone, at first, the cirripede 

 adheres to the surface of attachment; within these pro- 

 longations the cement-ducts are included. I have, moreover, 

 seen instances, as in Conchoderma aurita and in the male of 

 Ibla and Alcippe, in which these tubular prolongations, lined 

 internally by corium, were increased a little in length, so as 

 to form a trouser-like termination to the peduncle. That 

 the forked extremity should be a little more developed, and 

 so be converted into a pair of short tubular threads, cannot 

 be considered as very improbable. 



* This may be partially seen in the section, fig. 1, of Balanus, on the 

 same plate (25) with the figure of Proteolepas ; here (bearing in mind that 

 Balanus is a much modified form) (z) shows the pupal antennae, within which, 

 whilst young, the cement-ducts are included, and are directly continuous with 

 the layer of branching ovarian caeca (g), which are prolonged up to the ovaria 

 as a pair of simple tubes (only one being here represented), entering the body 

 above the upper margin of the prosoma (c). The prosoma of Balanus, I may add, 

 answers to the segment 2 1 in fig. 7 of Proteolepas ; (e) the mouth in Balanus, 

 of course corresponding with (ni) the mouth of Proteolepas; the segment ' c and 

 " J t of the latter, are in Balanus aborted or confluent, at least on the ventral surface; 

 and, lastly, the whole great shell of Balanus, the sack with its muscles and the 

 branchiae, and the opercular valves with their muscles, are all represented in 

 Proteolepas merely by the outer membrane of the two threads (g), which enter 

 the pupal antenna?. ! 



