168 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
other, are alleged to be mere trivialities in comparison "with the true 
criteria of a Vertebrate, viz. the presence of a coelom of a more primitive 
type than that of an Arthropod, and the existence of a notochord. He 
endeavours to answer this criticism. 
Preliminary Catalogue of the Processes concerned in Ontogeny.* 
Mr. C. B. Davenport has published the fourth of his studies in morpho- 
genesis. His object is to analyse the ontogenetic complex of processes 
into its simple elementary ones. He points out that he distinguishes 
between ontogenetic principles and ontogenetic processes. Under the 
former he includes such laws of development as terminal growth, repe- 
tition of parts, and bilateral symmetry in development. These he has 
not attempted to catalogue ; he is concerned only with ontogenetic pro- 
cesses which comprise the different elementary operations or actions 
exhibited in ontogeny. They may be divided into two classes, the grosser 
ontogenetic processes and the histogenetic processes. At present, 
the author deals with the former class only. These may be either 
general or special. Of the former, growth, nuclear division, and secre- 
tion are examples. The special ontogenetic processes affect the differ- 
entiation of the body. They may be classified first of all according to 
the form of the protoplasmic bodies in which they occur. These must 
exist either as isolated cells, or as larger multi-nucleated bodies. Of the 
latter we may recognise three classes: bodies extended chiefly in one 
direction, such as fibres, those which extend as a layer, and those in 
which the three dimensions are more nearly equal, and which form solid 
masses. 
The differential processes which the author recognises may be 
thus enumerated: — I. Processes occurring in mesenchyme, the term 
mesenchyme being used for all amoeboid migrating cells, of whatever 
origin: (1) Migration of nodal thickenings; (2) free migration of 
amoeboid bodies ; (3) aggregation of mesenchyme ; (4) attachment of 
the same ; (5) investment and inter-penetration ; (6) transportation ; 
(7) absorption. II. Processes occurring in protoplasmic threads or 
tubules : (1) Tropism, a term applied to certain processes which con- 
cern the direction which the elongated body takes ; (2) splitting ; 
(3) anastomosing; (4) union with other organs. III. Processes occur- 
ing in protoplasmic layers : (A) Processes affecting area, (a) Processes 
occurring in the wall of a sac. (1) Excessive growth of particular parts. 
(J3) Processes occurring in a plane or warped surface. (2) Formation of 
perpendicular folds ; (3) formation of folds in the plane of the area. 
(B) Processes affecting thickness. (4) Thickening ; (5) thinning. These 
two may be either general or local. (C) Processes affecting continuity. 
(6) Atrophy ; (7) detachment of a piece from a layer. (D) Processes 
affecting two or more layers. (8) Concrescence ; (9) perforation. 
IV. Processes occurring in a protoplasmic mass : (A) Affecting espe- 
cially change of volume. (B) Affecting especially change of form. 
(C) Affecting especially change in number. 
The author believes that his hypothetical interpretation of the onto- 
genetic processes will admit of being tested experimentally. Just as 
the control of the migration of amoeboid bodies in the adult has been 
* Bull. Mus. Comp. Zool., xxvii. (1895) pp. 173-99. 
