318 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the egg-envelope is thrown off very early, even while cleavage is still 
going on. Since cilia appear as early as the blastula-stage the embryo 
is very soon able to move freely and thus become a larva. In this way 
Patella resembles a Lamellibranch, but such early locomotion is not 
common among the gastropods, most of the larvae hatching at a much 
later stage." "In later stages the displacement of the blastophore 
(as shown by Patten in Patella) becomes much more striking and 
recalls the condition already described in connection with Dentalium." 
In certain stages "the Patella larva closely resembles the trochophore 
stage met with in the Lamellibranch." Korschelt says it is a striking 
fact that a few specially low forms of gastropods such as Haliotis and 
still more Patella and Fissurella are distinguished by a reduction of 
coils and the adoption of a flat cup-shaped shell. In youth the shell 
was, as in other gastropods, distinctly coiled. This is so in Fissurella, 
Cemoria, and other associated forms, but, as I have shown here, it is 
not so in regard to the two species of Acmaea studied. Korschelt 
regrets that the development of Patella was carried by Patten only to a 
stage at which the larva is still far removed from the shape of an adult. 
He speaks of Patella and its allies as one of the most lowly groups of 
gastro])ods. 
Walter K. Fisher, in his anatomy of Lottia gigantea, emphasizes the 
primitive character of the Acmaeidae when he says, "There is little 
foundation for Thiele's dictum that the single ctenidium of the mono- 
branchiate Docoglossa is a secondary structure and that the primary 
gill has degenerated. As a matter of fact nothing is known of the 
development of these forms while everything about the structure points 
to the fact that the existing ctenidium is not secondary. The nervous 
supply is very abundant and springs from the selfsame ganglion as does 
that of the corresponding gill of Haliotis which this investigator is so 
anxious to prove primitive and in a direct line of descent. Further- 
more the attachment of the gill by its base in the Acmaeidae is much 
more similar to the condition in the Chitons, than is that of Haliotis, 
where the gill is fastened alongside of the efferent vein. The passage 
of the blood in Lottia from the ctenidium into a pallial sinus, and thence 
into the heart is more primitive than the direct connection found in 
Haliotis, and again agrees more closely with the condition of affairs 
found in Chitons." 
Lankester (7), in his "INIollusca" in the Encyclopaedia Brittanica, 
says, "The eyes of the Limpet deserve mention as examples of the most 
