206 SUMMARY OF CURRENT RESEARCHES RELATING TO 



is epithelial, the subjacent club-shaped, yellow coloured portion is a 

 peripheral ganglion-cell. The epithelium of the rectum is peculiar. 

 The auditory sac includes two different types of cpitholial cell, one 

 wineglass-shaped, the other retort-like. 



IV. Muscular tissue. Tho muscle-fibres are surrounded by connec- 

 tive tissue. There is no sarcolcmma. Tho cardiac muscles have an 

 unusually large protoplasmic region round the nucleus, greater in mass 

 than the contractile substance. The contractile substance is a product 

 of the muscle-cell. The primitivo fibrils of tho contractile substance are 

 histogenctic homologues of the connective tissue fibrils. Unstriped 

 muscles aro found in adductors and in mantle. No true transverse 

 striation was found. Tho fibres multiply only from musclc-germ-cells, 

 which persist even in the adult organism. Tho division of the nucleus 

 of a fibre is a subordinate, persistent embryonic process. 



V. Nervous tissue. In the nervous system ganglionic and nerve-cells 

 have to bo distinguished. The former are starting-points for the nerve- 

 fibres. The latter lie imbedded between the primitive fibrils of the 

 nerve-fibres ; they produce the fibres. Tho fibres show no membrane or 

 myelin sheath ; they correspond to axial cylinders, or rather to Bemak's 

 fibres in vertebrates. Tho branching of the fibres is then described. 

 The long nuclei of the nerve-fibres or nerve-cells are, like those of tho 

 muscle-fibres, surrounded by a protoplasmic mass, continued in a long 

 process at the poles. H. Schultze confused these cells with connective- 

 tissue cells, which lie not in, but between the nerve-fibres. Between the 

 several ganglion-cells, fine processes of the connective tissue were 

 demonstrable. Dogiel's apolar ganglion-cells occur both in connection 

 with the cardiac muscles and elsewhere. The nerve-terminations inner- 

 vating the epithelial cells of the mantle-margin, end in minute round 

 plates. In the adductors, the nerve-terminations penetrate the fibres in 

 the nuclear regions. They consist of an axial thread or primitive fibril, 

 surrounded by a pale sheath, probably of interfibrillar substance. Only 

 the axial thread enters the muscle-fibre, the latter loses itself on tho 

 surface. The axial thread may be traced into the protoplasmic mass of 

 the muscle-fibres, and never seem to end in the contractile substance. 



Molluscoida. 

 o. Tunicata. 



Classification of Tunicata.* — Prof. E. van Beneden thinks that tho 

 discoveries of the last few years necessitate a revision of the classification 

 of Tunicates. He here confines himself to some critical notes, and the 

 formation of a new genus. The genus Ecteinascidia of Herdman shows 

 that the modes of reproduction cannot be taken as a basis of classification. 

 The author has lately been able to investigate Philippi's little-known 

 genus Bhopalsea, and with it he places E. crassa and E. fusca of Herdman. 

 For E. turbinate/,, in which there is no division of the body into thorax 

 and abdomen as in the preceding, a thin and not cartilaginous test, as well 

 as other differential characters justify the generic separation of this 

 species, with which E. diaphanis of Sluitcr may be associated. For tho 

 species E. rubricollis Prof, van Beneden proj)oses the new generic term 

 of Sluiteria ; the distinction may bo justified on the ground that its test 

 is provided with conoid papillre, and traversed by stolonial tubes (vessels 



* Bull. Acad. R. Sci. Belgr, hi. (1887) pp. 19-47. 



