ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
319 
Origin and Relationships of Arthropoda.* — Prof. N. Zograf has an 
essay on this subject. The most important points upon which he wishes 
to insist appear to be the following : — 
The cephalic invaginations of the embryos of all Arthropods are the 
remains of sense-organs which are identical with the cephalic sensory 
organs of Annelids, and are common to the ancestors of these animals. 
Future researches in the embryology of Arthropods should aim at 
the solution of the question of the existence in the embryo of the 
remains of segmental sensory organs. 
In the embryos of Myriopods, and probably in those of other 
tracheate Arthropods, there are traces of the nephridia of the first 
postoral pair as well as of the appendages which correspond to these 
nephridia. Future researches must determine the presence or absence 
of postoral papillce of the embryo, as well as their correspondence with 
the salivary glands or some other derivative of the primitive nephridia. 
The author thinks that the question of the homology between the ducts 
of the gonads of Chilognatka and the nephridia of the third and fourth 
segments of the Protracheata should be investigated. In his judgment 
the view that the Malpighian tubes are derived from nephridia is a pure 
hypothesis, the truth of which can only be asserted after detailed re- 
searches into the development of the Malpighian tubes of Myriopods and 
of the higher Arthropoda. Although some further research is needed, 
it appears probable that the elements from which the ducts of the gonads 
of Myriopods are derived owe their origin to the nephridia of annelidi- 
form ancestors. 
Prof. Zograf does not think that the difference in the histological 
structure of the nerve-chain is an obstacle against admitting the theory 
of the origin of the tracheate Arthropods from such ancestors ; some 
parts, indeed, of the nerve-chain of the lower Tracheates present traces 
of the primitive histological structure. If the opinion of some authors 
that the coxal pores of Peripatus and the Myriopoda are the remains of 
the setigerous pouches of Annelids shall be shown to be correct, the 
theory of the origin of Tracheata from an annelidiform ancestor will 
have one support. At any rate, this theory, as elaborated by Kennel, 
is based on a number of ascertained facts. 
The author is anxious to see the Crustacea ranged with the rest of 
the Arthropoda, and is of opinion that a revision of the embryogeny of 
Crustacea, from the point of view of their relationship to the other 
groups of Arthropods, is urgently needed. The most important pro- 
blems are the presence or absence in adult or embryonic Crustacea of 
traces of the organs proper to Annelids or their supposed ancestors — that 
is to say, of segmental sensory organs, of nephridia, and of the cephalic 
sensory organs which are so well developed in the Capitellidae. Before 
the hypothesis of the derivation of the Nauplius from the Trocho- 
sphaera can be taken to be correct, proofs must be found that the 
appendages of the Nauplius are homologous with those of Rotifers, or 
there must be a demonstration of the existence of remains of the ciliated 
ring or of a ring of separated nerve-cells or the existence of traces of 
the two cephalic nephridia which are found in Rotifers. 
* Congres Internat. de Zooh, II. i. (1892) pp. 278-96. 
