412 Dr. F. Miiller on a Hybrid Balanus. 
deners, regard their various peculiarities as so much better 
fixed, or so much less variable, the earlier they were acquired, 
the longer they have been inherited unchanged, it becomes 
intelligible that, above all, the characters proper to the primi- 
tive form persist, and that consequently, in the crossing of two 
species, these are more readily transferred to the hybrid than 
later-acquired peculiarities of the father or mother. 
From this point of view I think we shall be able to explain 
many peculiarities of hybrids and, vice versé, perhaps in ~ 
many cases to trace from the form of the hybrids to the 
primitive form of the genus,—the latter, of course, only with 
the greatest care; for the mere fact that the hybrids produced 
by males of one species with females of another do not agree 
with those produced by males of the second species with fe- 
males of the first, furnishes a proof that other circumstances 
aid in determining the form of the hybrids. 
EXPLANATION OF PLATE XX. 
Fig. 1. Specimens of Balanus armatus, seated upon Carijoa: c, carina ; 
r, rostrum. 
Fig. 2. Scutum of B. armatus, seen from without, with particularly large 
pits and distant strize of growth. 
Fig. 8. Another Restininiey broad) scutum, from within. 
Fig. 4. Hybrid of Balanus armatus and B. improvisus. 
Fig. 5. Scutum of B. improvisus, var. assimilis, from without. 
Fig. 6. The same scutum, from within. 
Fig. 7. Outline of the mouth in B. armatus. 
Fig. 8, Outline of the mouth in a hybrid of B. armatus and B. impro- 
visUs. 
Fig. 9. Outline of the mouth in B. improvisus, var. assimilis. 
Fig. 10. Labrum of B. armatus. 
Figs. 11-13. Labrum in three different individuals of B. emprovisus, var. 
assimilis. 
Fig. 14. Sete from the carinal side of the tergum in B. armatus. 
Fig. 15. Setze from the scutal side of the same piece. 
Fig. 16. Setee from the seutum in B. armatus. 
Fig. 17. Setee from the tergum in B. improvisus, var. assimilis. 
Fig. 18, Setz from the strie of growth on the tergum of B. tmprovisus, 
var. assimilis. 
Fig. 19. Anterior ramus of the third pair of cirri of B. armatus, from. 
within, wherefore only the teeth which project beyond the 
margin are visible. Ka 
Fig. 20. The same ramus from the hybrid, from without. : . 
Fig. 21. Ninth joint of the outer ramus of the third pair of feet in alarge — 
B. armatus, from without. . 
Fig. 22. Tenth joint of the outer ramus of the fourth pair of feet in B. 
armatus, from without. 
Fig. 23. Seventh joint of the outer ramus of the third pair of feet in the — 
ere rom without. ; 
y 
Fig. 24. The same joint of a B. improvisus, var. assimilis, from without. 
