620 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
important morphological features in which the Chiton resembles Nautilus 
is remarkable. These are: — (1) Bilateral symmetry ; (2) general charac- 
ters of the nervous system ; (3) the possession of paired metamerically- 
arranged ctenidia, of which, in some species, there is a tendency for those 
at the anterior end of the body to disappear ; (4) the traces of metamerism 
exhibited by the heart in some forms ; for example, Chiton magnijicus 
has four pairs of auriculo-ventricular openings. The general relations 
of the coelom and nephridia are much the same in both cases, and both 
have eggs developed in follicles. 
y. Gastropoda. 
Early Development of Limax/* — Mr. C. A. Kofoid’s object in study- 
ing the development of Limax was a desire to add something to our 
knowledge of the details of molluscan embryology, many of the results 
of which are vague and even contradictory. Limax seemed, for many 
reasons, to be a desirable object for his investigations, as the adults 
are readily procurable, and an abundant supply of eggs, whose age is 
approximately known, can be obtained from animals kept in confinement. 
The absence of a large amount of yolk leaves the eggs sufficiently 
translucent for examination in toto. Discussing, first, the nomenclature 
of spiral cleavage, the author points out that it was necessary to intro- 
duce, as he has done lately, f a new system of nomenclature, and he 
gives reasons which he thinks justify him in introducing it. In a 
general way it may be said that Limax has spiral cleavage of the typical 
form, the spirals alternating in successive cell-generations, right spirals 
resulting in the even generation, and left spirals in the odd. The 
mesoderm is derived from the left posterior quadrant, and, as in various 
other forms, the first mesoblast cell is d 7 ' 2 ; and an ephemeral, recurrent 
cleavage cavity appears at the two-cell stage, and recurs as late as the 
completion of the period of gastrulation. This cavity has an excretory 
function, and is induced by the environment of the egg. The primary 
mesoblast divides bilaterally, ultimately sinks below the general level, 
and forms two bilaterally placed mesodermal bands extending anteriorly. 
The formation of these bands precedes and accompanies gastrulation. 
The blastopore is at first broad and shallow, but it gradually deepens at 
the anterior end, and disappears from the posterior margin anteriorly, 
forming an elliptical pit on tlie median ventral surface. The lateral 
and anterior lips of this pit grow rapidly, and there is at the same time 
an accumulation of mesoderm in these regions, and a general readjust- 
ment of the axes of the embryo ; the opening leading into the archenteron 
assumes a position at what was the posterior margin of the blastopore. 
This remnant of the blastopore comes to lie in the anal region; the 
mouth breaks through at a later period upon the ventral surface of the 
embryo. It will be seen that the conclusions to which the author has 
arrived as to the fate of the blastopore in Limax agrestis are directly 
contradictory to those of Fol upon L. maximus, for according to him the 
blastopore becomes the permanent mouth. Mr. Kofoid thinks that Fol 
entirely overlooked the early stages in the history of the blastopore. 
The author deals in detail with the orientation of the embryo, critically 
* Bull. Mus. Comp. Zool., xxvii. (1895) pp. 35-118 (8 pis.). 
t See this Journal , 1894, p. 555. 
