Dr. H. Schaum on the Head and Segments in Insects. 173 



sulphur-yellow round the branchial orifice, continuous with a 

 stripe or blotch of the same colour above ; they are arranged in 

 short, ill-defined, branching systems, with the common orifices 

 indistinct. Diameter of mass two to two and a half inches. 



I met with this species on the under side of stones within 

 tide-marks, St. Peter's Port, Guernsey, in 1853. This and the 

 following species have the individuals more minute than is usual 

 in the genus. 



Botrylloides pusilla, u. sp. 



Common body encrusting, semitransparent, orange-flesh-co- 

 loured, with yellow marginal tubes. Individuals small, bright 

 orange-scarlet, consisting of a minute sprinkling of scarlet on a 

 yellow ground ; there is a yellow spot behind the branchial aper- 

 ture, and the anal aperture is also yellow; the individuals are 

 set in crowded double or treble rows, forming ill-defined systems. 

 Branchial sac with ten rows of stigmata. Diameter of mass 

 nearly two inches. Length of individuals half a line. 



A single specimen of this beautiful and very distinct Botiijl- 

 loides was got on the under side of a stone at Grand Havre, 

 Guernsey, in 1853. 



Figures of most of the species here described, along with 

 others not previously or hitherto imperfectly figured, will be 

 given in an illustrated Catalogue of British Timicata, now pre- 

 paring for the British Museum. 



EXPLANATION OF PLATE VIL 



Fig. \. A portion of the branchial sac of Ascidia parallelogramtna, highly 



magnified. 

 Fig. 2. Two spiral coils of the same, more highly magnified. 

 Fig. 3. A small portion of the branchial sac of Molgula arenosa, showing 



the cones in profile. 

 Fig. 4. Two of the cones seen in front. 



XIX. — On the Composition of the Head, and on the Number of 

 Abdominal Segments, in Insects. By Dr. H. Schaum. 

 [Plate VL] 

 As the opinion has lately gained much ground among the com- 

 parative anatomists of England, chiefly through the embryo- 

 logical researches of Prof. Huxley, that the head of the Arthro- 

 poda is made up of a number of segments, I desire to draw 

 attention to some facts which seem to militate against this view. 

 Prof. Huxley * admits, with regard to the greatest number of 



* " On the Agamic Reproduction and Morphology of Aphis," Trans. 

 Linn. Soc. xxii, p. 229 &c. 



