SOOLOQY AND BOTANY, MICROSCOPY, ETC. 41 



and left sides are concerned, with tliat of Milne-Edwards, and is exactly 

 the reverse of that of Savignj, Hancock, and Lacazo-Duthiers. The 

 dorsal surface looks upwards, the ventral downwards. The body is 

 divisible into a thorax, which comprises the branchiae, nervous system, 

 and buccal and cloacal orifices ; an abdomen, which contains the 

 digestive tube ; and a post-abdomen, in which are the gonads and the 

 heart. 



The first chapter deals with the colony. There is only slight 

 adhesion between the common or external tunic and the subjacent 

 epithelium ; but this adhesion is more marked in some regions than 

 elsewhere, as, for example, along the longitudinal lines, of which there 

 are generally ten on either side of the body, and in the region of the 

 buccal and cloacal orifices, where there is to be found the homologue of 

 the reflected tunic of the simple Ascidians, in the form of a fold. The 

 cloacal orifices of the various ascidiozooids do not open directly to the 

 exterior, but into ramified ducts, which may be called a common cloaca. 

 The anal " languettes " are not free, but are so placed as to keep the 

 canal widely open. The constitution of the external tunic of Fra- 

 garoides is quite similar to that of various simple Ascidians, but there 

 are no vacuoles. This tissue of cellulose is not, as most authors have 

 hitherto supposed, a product secreted externally by the epidermic layer, 

 but a transformed portion of the epidermic epithelium produces the 

 cellulose internally. The epidermis is made up of several layers of 

 cells, which give rise to cellulose. 



When a member of a colony is about to die its body commences to 

 break up in its anterior region; the boundaries of the cells become 

 effaced, and the nuclei disappear; these remains of dead animals 

 gradually disappear, because, as the author believes, the amoeboid cells 

 of the external tunic act as phagocytes. Another phenomenon of the 

 same kind is to be seen in the mode of disappearance of the yolk in the 

 urodele larva of this species. There is no trace of a colonial vascular 

 system. 



The yellow colour of the common tunic is solely due to the presence 

 of numerous microscopic algae, belonging, apparently, to the genus 

 Protococcus ; the orange-red colour of the Ascidians is the result of the 

 combination of the colour of the algae with that of the pigmented cells 

 of the animals. 



The second chapter deals with the body-v^all ; this is composed of 

 epidermis, a connective-muscular framework, and a peribranchial 

 epithelium ; the first of these consists of the external tunic and the sub- 

 jacent epidermal epithelium ; the framework is a mass of connective 

 tissue in which we may say that all the organs of the body are immersed ; 

 it is hollowed out by vast lacunae in which the blood of the Ascidian 

 circulates. The peribranchial epithelium has the same structure and 

 properties as the epidermal, save that it does not secrete cellulose. 



The buccal siphon is treated of in the third chapter ; the buccal 

 orifice is divided externally into lobes of a peculiar form, of which two 

 are median and six are lateral in position. The layer of connective 

 and muscular tissues is very rich in blood-lacunae, and is traversed in 

 all directions by muscular bundles ; of these there are, for the greater 

 part of the siphon, three layers, two longitudinal being separated by one 

 transverse. The tentacular crown consists of a fold of the internal wall 

 of the buccal siphon, which carries fourteen unequal tentacles. Ten of 



