318 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
formed, which soon frees itself and developes fibrillar substance in its 
centre. The lower part becomes the stomach and mid-gut. How far 
the hind-gut arises from another evagination of the atrium is undeter- 
mined. The mesoderm elements become connective-tissue and muscle- 
cells, and also form the gonads, whose paired rudiments lie laterally to 
the large ganglion. The process is thus comparable to gastrulation, for 
the mother animal supplies no endodermic rudiment. In this last 
respect the budding of Polyzoa differs markedly from that of Coelen- 
terata or Tunicata, where the endoderm plays an important part. 
Arthropoda. 
Morphology of Compound Eyes of Arthropods.^ — Mr. S. Watase 
describes the structure of the ommatidium in SeroliSy Talorchestia, 
CamharuSy Homarus, and Callinectes ; describes the compound eye of 
LimuluSy^ and discusses the phytogeny of the ommatidium. He comes 
to the conclusion that the structure of the ommatidium of the compound 
eye of Serolis shows that it may be reduced to a simple ectodermic 
invagination of the skin. The same interpretation may be applied to 
the other Crustacea mentioned, and finds a strong support in the fact 
that, in LimuluSy the ommatidium is an open pit of the skin. 
By supposing that the ommatidial pit of Limulus became deeper, and 
that this increase in depth was accompanied by modifications in the 
structure and arrangement of the component cells, it becomes probable 
that the ommatidium of the compound eye of an Arthropod is an inde- 
pendent invagination of the skin. If this be so, the unit of the 
compound eye is not so complex a structure as some have supposed, and 
the enormous increase in the number of the ommatidia is merely an 
example of the well-known phenomenon of the duplication of a single 
unit. 
a. Insecta. 
Early Stages in Development of Ova of Insects.}: — Dr. H. 
Henking commences a series of memoirs with an account of the ovum of 
Pieris brassicse, with remarks on the sperm and spermatogenesis. It is, 
however, unnecessary to give the details as the results attained are very 
much those already given for Musca vomitoria by the author and by 
Blocbmann.§ 
Abdominal Appendages in Hexapoda.|| — Herr E. Haase urges that 
the researches of various observers commencing with Kowalevsky in 
1871, justify the supposition that the existing Hexapoda are to be 
derived from polypodous myriopodiform ancestors. He brings together 
the observations made by various authors on abdominal appendages in a 
way which will probably be found very useful. 
Composition of Body of Blattidae.^ — The same author has made an 
investigation into the composition of the body of the cockroach and its 
allies. He recognizes in the mature embryo a frontal piece which bears 
* Stud Biol. Lab. John Hopkins Univ., iv. (1890) pp. 287-334 (7 pis.). 
t For a preliminary note, see this Journal, 1889, p. 747. 
X Zeitschr. f. Wiss. Zooh, xlix. (1889) [1890] pp. 503-64 (3 pis.). 
§ See this Journal, 1887, p. 743; 1888, p. 573. 
[1 SB. Ges. Naturf. Freunde, 1889, pp. 19-29. ^ T. e., pp. 128-36. 
