1904.] NATURAL SCIENCES OF PHILADELPHIA. 329 
vegetative pole (‘‘macromeres”’) and from which the ‘micromeres”’ 
arise; for these latter the small letters a, b, c and d are used. Child 
(1900) and Treadwell (1901) have been followed in giving coefficients to 
the macromeres also, to indicate their generation, this being desirable 
when dealing with an egg in which, after the first few cleavages, the 
‘“‘macromeres”’ are large in name only. “Thus A, B, C, and D form 
the four-cell stage. At their next division from A arises 1A and 1a; 
from B, 1B and 1b, etc.; 1A then divides into 2A and 2a, while la 
divides into la! and 1a?” (Treadwell). 
EARLIER WoRK ON OPISTHOBRANCH DEVELOPMENT. 
A rather large number of older investigators have worked upon 
Nudibranch larval development. Grant (1827) described the veligers 
of Aolis and Doris. In 1837 Sars discovered that the young of T’ri- 
tonia, Doris and Afolis possess a nautiloid shell; additional researches 
by the same investigator appeared in 1840 and 1845. Lovén (1839) 
described a number of Nudibranch larve together with those of other 
mollusks. Alder and Hancock’s magnificent monograph upon the 
British Nudibranchs appeared in 1845 and contains a good general 
account of the results thus far obtained upon the subject of Nudi- 
branch embryology. Reid in 1846 published an interesting paper upon 
the breeding habits of Doris, Goniodoris, Polycera, Dendronotus, Doto, 
etc., together with the constitution of the larve. An account of the 
_embryology of Tergipes by Nordman appeared in the same year, An 
extremely thorough account of the development of the Tectibranch 
Acteon by Vogt also appeared in 1846. In 1848 Koren and Danielssen 
described the early stages of a number of Nudibranchs from the Nor- 
wegian coast. Schneider (1858) described the veliger of Phyllorhée. 
Keferstein and Ehlers (1861) gave an account of some of the develop- 
mental stages of Aolis. 
The later investigations of Langerhans (1873), Lankester (1875), 
Trinchese (1880-1—7), Lacaze-Duthiers and Pruot (1887), Rho (1888), 
Mazzarelli (1892—3-5), Heymons (1893), Viguier (1898), Carazzi (1900), 
Guiart (1901), and other works upon Opisthobranch embryology, 
together with those of importance pertaining to the remaining mol- 
luscan groups, Annelids and Platodes, will be considered during the 
course of this paper. 
A good general account of spawning habits of Nudibranchs is found 
in Alder and Hancock’s “Monograph of the British Nudibranchiate 
Mollusea” (1845). 
