G6 Thirty-im st Report on the State Museum. 



NOTE ON THE EGGS OF THE TRILOBITE. 



By C. D. Walcott. 



Prof. Joachim Barrande gives a description of the supposed eggs of the Tri- 

 lobite, in the first volume of the Palaeontology of Bohemia.* He describes them 

 as having the form of black spherules; some two-thirds, and others four or six 

 millimetres in diameter. They occur mingled in the same beds with fragments 

 of Trilobites, and correspond in size with the first stages of development of the 

 species of Trilobites with which they are associated. In tho supplement to 

 Volume I, 1874, illustrations are given of groups of eggs, or ova, which were 

 found on the surface of the rock. In one instance, a group of cylindroid-shaped 

 ova was found within the glabella of a Trilobite — Barrandia crassa (Plate II, 

 fig. 6). In the description of the plate, the author states that he considers their 

 occurrence in this position purely accidental, and that they have the appearance 

 of the small bodies named Parca decipiens Flem., which have been considered 

 as the eggs of Grasteropods. The small bodies, forming the clusters or groups, 

 vary in'f'orm from ovoid, cylindroid, to discoid — retaining the same form in. each 

 individual group. The mode of occurrence of the groups of ova indicates that 

 they were deposited by the 'animal in the place and position found. Barrande 

 states that they are probably the ova of some Crustacean. 



The spheroidal bodies first mentioned are the only ones that have been con- 

 sidered as the ova of the Trilobite, the proof being their occurrence with the 

 fragments of Trilobites, and their correspondence in size with embryo forms of 

 the species with which they are associated. 



When cutting sections through the body of a Trilobite, Ceraurus pleurexan- 

 themus, I noticed, on an opaque, central, longitudinal section, numerous dark, 

 round and oblong, minute spots on the light-colored back-ground of calc-spar, 

 which filled the visceral cavity between the dorsal shell, hypostoma and ventral 

 membrane. Upon cutting off a section, and rendering it transparent, I saw that 

 the dark spots were the ova of the Trilobite. Subsequently several sections 

 were obtained, showing the ova in various positions within the visceral cavity. 

 In section Number 1, the Trilobite rests on its back, with the head and three 

 anterior segments of the thorax curving upward The hypostoma is in place, 

 separated, at the posterior end, from the dorsal shell of the head by a distance 

 of four mm. A thin membrane is attached to the posterior margin ; it passes 

 one-half the distance toward the dorsal shell, where it joins the ventral mem- 

 brane, which extends beneath the thorax five mm., terminating at the third seg- 

 ment. The remaining portion of the visceral cavity having been destroyed, the 

 rock fills the space to the dorsal shell. The ventral membrane is corrugated or 

 folded beneath each segment. The space between the dorsal shell and the ven- 

 tral membrane, two mm. wide, is filled with the ova, which, also, has pressed 

 into the cavity of the head, between the dorsal shell and the hypostoma, filling 

 about one-fourth of it. Over two hundred eggs are to be seen in this section. 

 The transverse section of an egg is round, averaging one-fourth of a mm. in 

 aiameter. The longitudinal section is oblong-oval or cylindroid, half of a 

 mm. in diameter. Those cut obliquely show various intermediate forms. A 

 second section of the same Trilobite, cut on a line with the pleural lobes, shows 



* SysUme Siluricn du Centre <ie la, Boheme. Tar Joachim Barrande. le. Partic. lleeherches 

 Paleoulologicjue.-;, vol. 1 ; Ciustaoes ; Trilobites, 1852, 



