. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. I04 BIOLOGICAL LECTURES. jnuc Extending the comparison into the later larval stages, we see that this difference still persists, and is even more noticeable than in the earlier. In the larva of AmpJiitj-ite of forty hours there is a very marked development of meso- dermal and trunk ectodermal tissue, or, in other words, a very large amount of material derived from the descendants of 2d and ^J-d (Fig. II, AmpJiitrite of forty-four hours, from Mead). AmpJiitrite has four well-marked body segments,
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. I04 BIOLOGICAL LECTURES. jnuc Extending the comparison into the later larval stages, we see that this difference still persists, and is even more noticeable than in the earlier. In the larva of AmpJiitj-ite of forty hours there is a very marked development of meso- dermal and trunk ectodermal tissue, or, in other words, a very large amount of material derived from the descendants of 2d and ^J-d (Fig. II, AmpJiitrite of forty-four hours, from Mead). AmpJiitrite has four well-marked body segments, with strong setae on two of them (ecto- dermal structures which have arisen from 2d), and, according to Dr. Mead, well-developed mesodermal tissue lining the gut and body wall. To be* noted, also, is the relatively small development of the umbrella portion (the portion in front of the prototroch) and the extreme width of the prototroch itself. The large mucous glands and the " proble- matic bodies" of Mead occupy a large part of the surface of the um- brella, the former extending back into the subumbrella portion. Turning now to Podarke, we find a very different condition of affairs. The most noticeable feature is the complete lack of any trace of segmentation. The subumbrella has elongated con- siderably, but shows no trace whatever of a division into somites. The umbrella is relatively much larger than in AmpJiitrite, a fact which is undoubtedly correlated with the unusual development of the cells compfising the cross in the former animal. I have not succeeded in finding any mucous glands, but what are prob- ably identical with Mead's "problematic bodies" and Wilson's " frontal bodies" are found lying just in front of the small eye spot on either side {pj-ob., Fig. 12, Podarke of forty-two hours).. Fig. II.— Ainphitrite{\^x Mead), forty-four Please note that these images are extracted from scanned page images that may have been digit
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