28 
W. E. AGAR. 
syndesis, on the other hand, covers a wider range, and may 
be applied to all those other forms of conjugation in which 
the chromosomes are united end to end. The Copepod tetrad 
illustrates the simplest type of this, which is supposed by 
Piickert, Hacker, etc., to be produced by the junction (or 
non-separation during segmentation of the spireme) of pairs 
of chromosomes end to end, the transverse joint of the tetrad 
representing their point of contact, and the longitudinal one 
the split which runs through both chromosomes; In 1903 
Montgomery attempted to show that the loops, rings, etc., of 
vertebrates (especially Amphibia) are of essentially the same 
structure, formed by the bending round of the two limbs 
(conjugating chromosomes) to form the rings, etc. Meta- 
phase I thus separates whole chromosomes, which divide 
longitudinally in metaphase II. In 1905 Farmer and Moore 
independently came to the same conclusion for vertebrates 
(Elasmobranchs) and many other forms. Theirs is essentially 
a metasyndetic scheme. 
If the theory of parasyndesis were established it would 
have a possible great significance for theories of heredity, for 
it allows of an extremely intimate union of the chromosomes, 
during which condition it is conceivable that an interchange 
of particles might take place (like the interchange of micro- 
nuclei between a pair of conjugating Ciliates). This would 
remove an often expressed difficulty of correlating Mendelian 
phenomena with cytological observation, namely, that the 
number of independently transmissible allelomorphs is 
often certainly much larger than the number of gametic 
chromosomes. In metasyndesis this intimate physiological 
union can play no part except as an accidental and only 
occasional result of a specially pronounced “second contrac- 
tion.” There is, for instance, no room for it in any of the 
older metasyndetic accounts, nor in Montgomery's scheme for 
Hesmoguathus fuscus or Farmer and Moore's Peri- 
planeta, though it might occur in Graltonia, according to 
the account given by Digby, who accepts Farmer and Moore's 
scheme. 
