ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
49 
The memoir commences with a series of chapters on the anatomy of 
the various organs, and is followed by a systematic review, in which the 
following genera are recognized : — Oncidium (emend.), Oncis g. n., 
Oncidiella, Peronina g. n., and Oncidina ; a systematic table gives the 
chief points of difference between them, and descriptive accounts follow 
of the thirty-two constituent species. 
Embryology of Chiton.* — Mr. M. M. Metcalf gives an account of 
the development of Chiton , as studied in two species collected at 
Jamaica. In the segmentation most of the divisions are of the radial 
type, but in some cases the cells, instead of dividing meridionally and 
subsequently shifting, divide in the first case obliquely and reach their 
definite position without any subsequent shifting. This the author 
regards as a cenogenetic modification of the radial type of segmentation ; 
it is due either to the simplification of development by acceleration or 
to crowding. 
The blastopore is formed at the vegetative pole, and is at first quad- 
rangular with a club-shaped furrow extending from its anterior edge 
forward along the mid-ventral line to the velum ; this furrow disappears. 
The blastopore sends out an anterior slit-like process, the posterior 
portion closes, and the anterior part moves still further forward to lie 
just behind the velum. The mouth forms by the direct re-opening of 
the blastopore. 
The phenomena of gastrulation in Chiton suggest comparison with 
Peripatus ; but to the interesting question whether the resemblances are 
fundamental or secondary it does not seem possible to give a definite 
answer. 
Index to the Zoologischer Anzeiger.f — Prof. J. V. Carus has had 
prepared an index to volumes xi.-xv. of his valuable journal ; it is very 
full and has but few errors. With the preceding index to the first ten 
volumes, and Dr. Taschenberg’s continuation of the 1 Bibliotheca 
Zoologica ’ the zoologist, if not fully “ up to date ” with his literature, 
is now admirably supplied up to the end of 1892. 
8. Lamellibranchiata. 
Muscle-Fibres of Mollusca.J— Herr Fh. Knoll describes those 
muscle-fibres in various Lamellibranehs which exhibit double oblique 
striation, and agrees with Engelmann that the appearance is referable to 
a contraction-process, and that the more strongly refractive particles 
are disposed in two distinct spiral systems, not in one, as Fol and 
Ballowitz have maintained. He leaves it doubtful whether these 
particles retain their spiral arrangement in completely relaxed fibres. 
The striae are not due to homogeneous fibrils, but to rows of “ Dis- 
diaklast ” groups of great mobility arranged in a fibril-like manner. 
The fibres are regarded as transitional towards the cross-striped type. 
In Eledone, Knoll has found transitions between fibres with a marked 
double oblique striation and those with longitudinal striation, i. e. with 
striae almost parallel to the longitudinal axis. Perhaps they are only 
contraction states of one type. M 
* Stud. Biol. Lab. John Hopkins Univ., v. (1893) pp. 249-67 (2 pis.). 
+ Register zum Zoologischen Anzeiger, Jahrgang xi.-xv., 8vo, Leipzig, 1893, 329 
pp. (double cols.). % SB. K. Akad. Wiss. Wien, ci. (1892) pp. 498-514 (2 pis.). 
1894 E 
