JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
OCTOBER 1896. 
TRANSACTIONS OF THE SOCIETY. 
IX.— On the Occurrence of Endocysts in the Genus Thalassiosira. 
By Thomas Comber, F.R.M.S. 
(Bead 21 st October , 1896.) 
Plate XI. 
In 1864 Mr. Lander observed the formation, within the frustule of 
various species of Bacteriastrum and Chsetoceros, of what he termed 
“ a gonidium or sporangium, consisting of a cell with two rounded 
ends, and a connecting hoop, one end being smaller than the other.” 
He supposed this to be a phase of a special method of reproduction ; 
and described it as originating in the condensed endochrome of the 
frustule secreting a siliceous envelope, more or less spinous, within 
which highly refractive globules were formed. The frustules then 
break up, and set free the enclosed bodies. e£ The contents of the 
sporangium soon escape ” ; but he was not able to follow out the further 
processes they undergo towards the reproduction of the original form. 
He suggested that many, if not all, the species in the genera Gonio- 
thecium , Omplialotheca , and Hercotheca, and perhaps in Dicladia , 
Periptera, and Syndendrium , would “ turn out to be sporangial bodies 
of species of Chsetoceros.” 
To some extent this surmise has proved correct. In the ‘ Challenger ’ 
collections, for instance, Count Castracane found, within the frustules 
of a Chsetoceros , the form Dicladia capreolus Ehr., well known from 
its frequent occurrence in guano. Other instances of the formation of 
these bodies have been recorded by Dr. Cleve, who, however, proposes 
for them the term “ endocysts and this appears to be a better name, 
as their real function is still quite uncertain. 
EXPLANATION OF PLATE XI. 
Fig. 1. — Side view of valve x 1000. 
„ 2. ,, ofendocyst x 1000. 
„ 3 and 4.— Filament without endocysts x 509. 
,, 5 and 6. „ with endocysts X 500. 
„ 7. — Front view of cndccyst x 500. 
2 M 
1896 
