DEVELOPMENT OF LIMULUS POLYPHEMUS. 187 



probably very similar to those of Limulns, as they could not have united sexually, and 

 the eggs were probably laid in the sand or mud, and impregnated by the sperm cells of 

 the male, floating free in the water. As previously stated, the female Limulus burrows 

 beneath the sand or mud and leaves her eggs loose in the burrow, covered by a few inches 

 of sand, etc. This is an exception to the usual mode of oviposition in the Crustacea. The 

 only other exceptions known to us are the land crabs (Gecarcinus) of the West Indies, 

 which go to the sea and leave their eggs in the water, and then go back to the land, and 

 Squilla, which deposits her spawn in shoal water passages in the foi-m of thin, round, yel- 

 low plates, according to Miiller, but he adds that she remains by them aiding their devel- 

 opment by driving a stream of water through the hole for her own respiration. 



The muscular system of the Trilobites must have been highly organized, as in Limulus, 

 as, like the latter, they probably lived by burrowing in the mud and sand, using the shovel- 

 like expanse of the head in digging in the shallow palseozoic waters after worms and 

 stationary soft-bodied invertebrates, so that we may be warranted in supposing that the 

 alimentary canal was constructed on the type of that of Limulus, with its large, powerful 

 gizzaixl and immense liver. 



From these considerations, and the fact that the eggs have been found loose in the beds 

 associated with remains of the animals themselves, we should suppose that the Trilobites 

 lived in shallow water and near the shore, as Limulus does at the present day. Barrande 

 supposed that they lived in deep water and swam on the surface of the sea, but the solid 

 integument and flattened broad body would seem to have been sufficient to indicate that 

 they frequented the bottom. Bm-meister was probably more correct in supposing that 

 they lived in shallow water. 



Classification of the Branchiopoda. In his celebrated work on the "Organization of the 

 Trilobites," Burmeister sagaciously concludes "that tlie Trilobites were a peculiar flimily of 

 Crustacea, nearly allied to the existing Phyllopoda, approaching this latter family most 

 nearly in its genus Branchipus, and forming a link connecting the Phyllopoda vnth. the 

 Poecilopoda," but on account of the " varying numerical proportion of their thoracic rings," 

 he thinks the relation is one of analogy and not of affinity, and that the Trilobites are 

 equivalent to all the Entomostraca [Aspidostraca). With the ideas in the sentence 

 quoted, our own review of the structure of the living Branchiopoda and the embryology 

 of Limulus, and a comparison with the Trilobites, lead us to fully coincide ; but we would 

 go farther and include the Merostomata with the Branchiopoda, as together forming a 

 division, (perhaps a subclass, equivalent to the Decapoda). Burmeister has demonstrated 

 very clearly the close homology of the head of the Trilobites with that of the Phyllopoda, 

 especially the structure and relations of the hypostoma and the frontal "doublure." The 

 parts corresponding to the jaws and first pair of antenniform maxillipedes of the Phyllo- 

 pods, are not preserved in the Trilobites. I would venture to predict from the structure 

 of Limulus that we shall look in vain for antennre in the Trilobites, i. e., any articulated 

 organs of sense arising in front of the mouth ; while it is not improbable that a pair of 

 antenniform maxillipedes, such as those of Apus, existed, together with pairs of jaws, like 

 those of Branchipus and Apus, or ambulatory appendages, formed at the base like jaws, as 

 in Limulus, on each side of the mouth. 



The presence of a pair of maxillipedes was suggested by the observations of Mr. H. 



